Onium salts, photoacid generators for resist compositions, resist compositions, and patterning process

ABSTRACT

Onium salts of the formula (1) are novel.                    
     R 1  is C 1-10  alkyl or C 6-14  aryl, R 2  is H or C 1-6  alkyl, p is an integer of 1 to 5, q is an integer of 0 to 4, p+q=5, R 3  is C 1-10  alkyl or C 6-14  aryl, M is a sulfur or iodine atom, and “a” is equal to 3 or 2. A chemical amplification type resist composition comprising the onium salt as a photoacid generator is suited for microfabrication, especially by deep UV lithography because of many advantages including improved resolution, minimized line width variation or shape degradation even on long-term PED, minimized defect after coating, development and stripping, and improved pattern profile after development.

This invention relates to novel onium salts, photoacid generators forresist compositions, resist compositions comprising the novel oniumsalts, and a patterning process using the same. The resist compositions,especially chemical amplification type resist compositions are sensitiveto such radiation as UV, deep UV, electron beams, x-rays, excimer laserbeams, y-rays, and synchrotron radiation and suitable for themicrofabrication of integrated circuits.

BACKGROUND OF THE INVENTION

While a number of efforts are currently being made to achieve a finerpattern rule in the drive for higher integration and operating speeds inLSI devices, deep-ultraviolet lithography is thought to hold particularpromise as the next generation in microfabrication technology.

One technology that has attracted a good deal of attention recentlyutilizes as the deep UV light source a high-intensity KrF excimer laser,especially an ArF excimer laser featuring a shorter wavelength. There isa desire to have a microfabrication technique of finer definition bycombining exposure light of shorter wavelength with a resist materialhaving a higher resolution.

In this regard, the recently developed, acid-catalyzed, chemicalamplification type resist materials are expected to comply with the deepUV lithography because of their many advantages including highsensitivity, resolution and dry etching resistance. The chemicalamplification type resist materials include positive working materialsthat leave the unexposed areas with the exposed areas removed andnegative working materials that leave the exposed areas with theunexposed areas removed.

In chemical amplification type, positive working, resist compositions tobe developed with alkaline developers, an alkali-soluble phenol or aresin and/or compound in which carboxylic acid is partially or entirelyprotected with acid-labile protective groups (acid labile groups) iscatalytically decomposed by an acid which is generated upon exposure, tothereby generate the phenol or carboxylic acid in the exposed area whichis removed by an alkaline developer. Also, in similar negative workingresist compositions, an alkali-soluble phenol or a resin and/or compoundhaving carboxylic acid and a compound (crosslinking agent) capable ofbonding or crosslinking the resin or compound under the action of anacid are crosslinked with an acid which is generated upon exposurewhereby the exposed area is converted to be insoluble in an alkalinedeveloper and the unexposed area is removed by the alkaline developer.

On use of the chemical amplification type, positive working, resistcompositions, a resist film is formed by dissolving a resin having acidlabile groups as a binder and a compound capable of generating an acidupon exposure to radiation (to be referred to as photoacid generator) ina solvent, applying the resist solution onto a substrate by a variety ofmethods, and evaporating off the solvent optionally by heating. Theresist film is then exposed to radiation, for example, deep UV through amask of a predetermined pattern. This is optionally followed bypost-exposure baking (PEB) for promoting acid-catalyzed reaction. Theexposed resist film is developed with an aqueous alkaline developer forremoving the exposed area of the resist film, obtaining a positivepattern profile. The substrate is then etched by any desired technique.Finally the remaining resist film is removed by dissolution in a removersolution or ashing, leaving the substrate having the desired patternprofile.

The chemical amplification type, positive working, resist compositionsadapted for KrF excimer lasers generally use a phenolic resin, forexample, polyhydroxystyrene in which some or all of the hydrogen atomsof phenolic hydroxyl groups are protected with acid labile protectivegroups. Onium salts such as iodonium salts and sulfonium salts,bissulfonyldiazomethane compounds, and N-sulfonyloxyimide compounds aretypically used as the photoacid generator. If necessary, there are addedadditives, for example, a dissolution inhibiting or promoting compoundin the form of a carboxylic acid and/or phenol derivative having amolecular weight of up to 3,000 in which some or all of the hydrogenatoms of carboxylic acid and/or phenolic hydroxyl groups are protectedwith acid labile groups, a carboxylic acid compound for improvingdissolution characteristics, a basic compound for improving contrast,and a surfactant for improving coating characteristics.

Onium salts as shown below are advantageously used as the photoacidgenerator in chemical amplification type resist compositions, especiallychemical amplification type, positive working, resist compositionsadapted for KrF excimer lasers because they provide a high sensitivityand resolution and are free from storage instability as found with theN-sulfonyloxyimide photoacid generators.

Since a finer pattern size is required, even the use of such photoacidgenerators gives rise to many problems including low resolution, lowenvironmental stability, and the formation of insoluble or difficultlysoluble foreign matter upon development with an alkaline developer orremoval of the resist with a solvent.

Of these problems, improvements in resolution are made by introducinginto a resin acid labile groups which are more prone to scission by anacid, or adding a basic compound, or modifying processing conditions.

It is known from JP-A 8-123032 to use two or more photoacid generatorsin a resist material. JP-A 11-72921 discloses the use of aradiation-sensitive photoacid generator comprising in admixture acompound which generates a sulfonic acid having at least three fluorineatoms upon exposure to radiation and a compound which generates afluorine atom-free sulfonic acid upon exposure to radiation, therebyimproving resolution without inviting nano-edge roughness and filmsurface roughening. However, we empirically found that these resistcompositions are unsatisfactory in resolution and in the effect ofeliminating the foreign matter on the pattern upon development.

For the purpose of improving the resolution upon microfabrication, JP-A6-148889 discloses a positive photosensitive composition comprising apolyfunctional enol ether compound and an alkali-soluble resin astypified by polyhydroxystyrene, which are thermally crosslinked on asubstrate, followed by exposure to radiation and PEB to provide adesired pattern. JP-A 6-266112 discloses a photosensitive resistcomposition comprising a photosensitive acid generator and a polymercomposed of hydroxystyrene and an acrylate and/or methacrylate. Thesecompositions are unsatisfactory in resolution and pattern profile.Substantial sliming upon post-exposure delay (PED) is also a problem.

The environmental stability is generally divided into two categories.One environmental stability is related to the deactivation of aphoto-generated acid by an air-borne base above the resist film or abase beneath the resist film and on the substrate. This phenomenon isoften seen when a photoacid generator capable of generating an acidhaving a high acid strength is used. It is expected that this problem issolved by introducing into the resin acid labile groups which are moreprone to scission by acid or by lowering or weakening the acid strengthof the photo-generated acid. The other environmental stability is thatwhen the period from exposure to post-exposure baking (PEB) isprolonged, which is known as post-exposure delay (PED), thephoto-generated acid diffuses in the resist film so that aciddeactivation may occur when the acid labile groups are less susceptibleto scission and acid decomposition may take place when the acid labilegroups are susceptible to scission, often inviting a change of thepattern profile in either case. For example, this invites a narrowing ofthe line width in the unexposed area in the case of chemicalamplification type, positive working, resist compositions having acidlabile groups, typically acetal groups.

As mentioned above, for achieving a high resolution, the resin shouldhave introduced therein acid labile groups which are more prone toscission, and the photoacid generator should desirably generate a lessdiffusible acid. The less diffusible acids under investigation arealkylsulfonic acids such as 10-camphorsulfonic acid. The alkylsulfonicacids, however, are weak in acid strength as compared with theconventionally used fluorinated alkylsulfonic acids and arylsulfonicacids, and such low acid strength must be compensated for by thequantity of acid. In order that a more quantity of acid be generated,the exposure time must be increased, often leading to poor productivity.

Addressing this problem, JP-A 6-199770, 9-244234 and 9-258435 discloseresist compositions using photoacid generators in the form ofarylsulfonic acids having an alkyl, carbonyl or carboxylate groupintroduced therein.

However, we empirically found that the direct introduction of a carbonylor carboxylate group into a benzene ring is effective for suppressingthe diffusion of the generated acid, but undesirably increases the lightabsorption near 248 nm of the photoacid generator and that theintroduction of an alkyl group can undesirably leave defect (residue)upon development.

With respect to the defect left upon alkali development and/or removalof the resist film with a solvent, a variety of factors includingphoto-decomposed products of the photoacid generator, non-decomposedcompound (that is the photoacid generator as such) and low soluble resinare considered, and none of these factors have been identifiedresponsible. However, the defect is probably correlated to thesolubility or affinity of the photoacid generator in the developer(aqueous solution) or remover solvent and the solubility or affinitythereof in the resin.

The photoacid generator in resist material is required to meet a fullyhigh solubility in (or compatibility with) a resist solvent and a resin,good storage stability, non-toxicity, effective coating, a well-definedpattern profile, PED stability, and no defect left during patternformation after development and upon resist removal. The conventionalphotoacid generators, especially those photoacid generators capable ofgenerating alkylsulfonic acids and arylsulfonic acids do not meet all ofthese requirements.

As the pattern of integrated circuits becomes finer in these days, ahigher resolution is, of course, required, and he problems of line widthvariation by PED and defect after development and resist removal becomemore serious.

SUMMARY OF THE INVENTION

An object of the invention is to provide a novel onium salt for use in aresist composition, especially of the chemical amplification type, suchthat the resist composition ensures a high resolution and a well-definedpattern profile after development and minimizes the defect (residue)left after development and resist removal. Another object of theinvention is to provide a photoacid generator for resist compositions, aresist composition comprising the onium salt, and a patterning processusing the same.

We have found that by using an onium salt of the general formula (1),especially a sulfonium salt of the general formula (1a) or (1a′) or aniodonium salt of the general formula (1b), to be defined below, as thephotoacid generator in a resist composition, there are achieved a numberof advantages including storage stability, effective coating, minimizedline width variation or shape degradation during long-term PED,minimized defect left after coating, development and resist removal, awell-defined pattern profile after development, and a high resolutionenough for microfabrication, especially by deep UV lithography.

Herein R¹ is a substituted or unsubstituted, straight, branched orcyclic alkyl group of 1 to 10 carbon atoms or a substituted orunsubstituted aryl group of 6 to 14 carbon atoms. R² which may be thesame or different is hydrogen or a substituted or unsubstituted,straight, branched or cyclic alkyl group of 1 to 6 carbon atoms. Letterp is an integer of 1 to 5, q is an integer of 0 to 4, p+q=5. R³ whichmay be the same or different is a substituted or unsubstituted,straight, branched or cyclic alkyl group of 1 to 10 carbon atoms or asubstituted or unsubstituted aryl group of 6 to 14 carbon atoms. M is asulfur or iodine atom, and “a” is equal to 3 when M is sulfur and equalto 2 when M is iodine.

Herein R¹, R², p, q and R³ are as defined above.

Herein R¹, R², p and q are as defined above, G is an acid labile grouphaving an oxygen atom attached thereto or R²O— or (R²)₂N—, g is aninteger of 0 to 4, h is an integer of 1 to 5, g+h=5, e is an integer of1 to 3, f is an integer of 0 to 2, and e+f=3.

Herein R¹, R², p and q are as defined above.

When the onium salt of formula (1) is used in a chemical amplificationtype resist composition as the photoacid generator, a resist imagefeaturing a high resolution and a wide range of focal depth isobtainable due to the effect of sulfonate sites. Owing to an adequatedegree of diffusion, the degradation of a pattern profile by PED isminimized. Owing to the polarity of sulfonate groups, the foreign matterleft after alkali development and resist removal is minimized.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Onium Salt

In the first aspect, the invention provides a novel onium salt having asubstituted or unsubstituted alkyl or arylsulfonyloxybenzenesulfonateanion of the following general formula (1).

Herein R¹ is a substituted or unsubstituted, straight, branched orcyclic alkyl group of 1 to 10 carbon atoms or substituted orunsubstituted aryl group of 6 to 14 carbon atoms. R² which may be thesame or different is hydrogen or a substituted or unsubstituted,straight, branched or cyclic alkyl group of 1 to 6 carbon atoms. Letterp is an integer of 1 to 5, q is an integer of 0 to 4, satisfying p+q=5.R³ which may be the same or different is a substituted or unsubstituted,straight, branched or cyclic alkyl group of 1 to 10 carbon atoms orsubstituted or unsubstituted aryl group of 6 to 14 carbon atoms. M is asulfur or iodine atom, and “a” is equal to 3 when M is sulfur and equalto 2 when M is iodine.

Specifically, the invention provides a novel sulfonium salt having asubstituted or unsubstituted alkyl or arylsulfonyloxybenzenesulfonateanion of the following general formula (1a) or (1a′).

Herein R¹, R², p, q and R³ are as defined above.

Herein R¹, R², p, and q are as defined above. G is an acid labile grouphaving an oxygen atom attached thereto or R²O— or (R²)₂N—, g is aninteger of 0 to 4, h is an integer of 1 to 5, g+h=5, e is an integer of1 to 3, f is an integer of 0 to 2, and e+f=3.

Specifically, the invention also provides a novel iodonium salt having asubstituted or unsubstituted alkyl or arylsulfonyloxybenzenesulfonateanion of the following general formula (1b).

Herein R¹, R², p, and q are as defined above.

In formulae (1), (1a), (1a′) and (1b), R¹ stands for substituted orunsubstituted, straight, branched or cyclic alkyl groups of 1 to 10carbon atoms or substituted or unsubstituted aryl groups of 6 to 14carbon atoms, and the R¹ groups may be the same or different.Illustrative, non-limiting, examples of the substituted orunsubstituted, straight, branched or cyclic alkyl groups of 1 to 10carbon atoms include methyl, ethyl, n-propyl, sec-propyl, n-butyl,sec-butyl, iso-butyl, tert-butyl, n-pentyl, sec-pentyl, cyclopentyl,n-hexyl, cyclohexyl, and groups represented by the following formulae.

Illustrative, non-limiting, examples of the substituted or unsubstitutedaryl groups of 6 to 14 carbon atoms include phenyl, 4-methylphenyl,4-ethylphenyl, 4-methoxyphenyl, 4-tert-butylphenyl, 2,4-dimethylphenyl,2,4,6-trimethylphenyl, 2,4,6-triisopropylphenyl, 4-fluorophenyl,pentafluorophenyl, 1-naphthyl and 2-naphthyl.

In formulae (1), (1a), (1a′) and (1b), R² stands for hydrogen orstraight, branched or cyclic alkyl groups of 1 to 6 carbon atoms, andthe R² groups may be the same or different. Illustrative, non-limiting,examples of the straight, branched or cyclic alkyl groups includemethyl, ethyl, n-propyl, sec-propyl, n-butyl, sec-butyl, iso-butyl,tert-butyl, n-pentyl, sec-pentyl, cyclopentyl, n-hexyl, and cyclohexyl.Also included are substituted alkyl groups, for example, oxo- andhydroxy-substituted alkyl groups such as 2-oxopropyl, 2-oxocyclopentyl,2-oxocyclohexyl, 2-hydroxycyclopentyl and 2-hydroxycyclohexyl. Informulae (1), (1a) and (1a′), R³ stands for substituted orunsubstituted, straight, branched or cyclic alkyl groups of 1 to 10carbon atoms or substituted or unsubstituted aryl groups of 6 to 14carbon atoms, and the R³ groups may be the same or different. Exemplaryof R³ are straight, branched or cyclic alkyl groups such as methyl,ethyl, n-propyl, sec-propyl, n-butyl, sec-butyl, iso-butyl, tert-butyl,n-pentyl, sec-pentyl, cyclopentyl, n-hexyl, and cyclohexyl; substitutedalkyl groups, for example, oxo- and hydroxy-substituted alkyl groupssuch as 2-oxopropyl, 2-oxocyclopentyl, 2-oxocyclohexyl,2-hydroxycyclopentyl and 2-hydroxycyclohexyl; and unsubstituted arylgroups and alkyl-, alkoxy-, amino- and alkylamino-substituted arylgroups such as phenyl, 4-methylphenyl, 4-ethylphenyl, 4-methoxyphenyl,4-tert-butylphenyl, 4-tert-butoxyphenyl, 4-cyclohexylphenyl,4-cyclohexyloxyphenyl, 2,4-dimethylphenyl, 2,4,6-trimethylphenyl,2,4,6-triisopropylphenyl, 3,4-bis(tert-butoxy)phenyl,4-dimethylaminophenyl, 1-naphthyl and 2-naphthyl, though not limitedthereto. Letter p is an integer of 1 to 5, q is an integer of 0 to 4,satisfying p+q=5. In formula (1), M is a sulfur or iodine atom, and “a”is equal to 3 when M is sulfur and equal to 2 when M is iodine.

In formula (1a′), G is an acid labile group having an 5 oxygen atomattached thereto or an alkoxy group: R²O— or a group: (R²)₂N— wherein R²is as defined above, g is an integer of 0 to 4, h is an integer of 1 to5, g+h=5, e is an integer of 1 to 3, f is an integer of 0 to 2, ande+f=3. The acid labile group having an oxygen atom attached thereto arepreferably those of phenolic hydroxyl groups whose hydrogen atoms arereplaced by groups of the following general formulae (4) to (7),non-cyclic tertiary alkyl group of 4 to 20 carbon atoms, preferably 4 to15 carbon atoms, trialkylsilyl groups whose alkyl groups each have 1 to6 carbon atoms, oxoalkyl groups of 4 to 20 carbon atoms, oraryl-substituted alkyl groups of 7 to 20 carbon atoms, though notlimited thereto.

Herein R¹⁰ and R¹¹ are independently hydrogen or straight, branched orcyclic alkyl groups of 1 to 18 carbon atoms, preferably 1 to 10 carbonatoms, for example, methyl, ethyl, propyl, isopropyl, n-butyl,sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl andn-octyl. R¹² is a monovalent hydrocarbon group of 1 to 18 carbon atoms,preferably 1 to 10 carbon atoms, which may have a hetero atom (e.g.,oxygen atom), for example, straight, branched or cyclic alkyl groups,and such groups in which some hydrogen atoms are replaced by hydroxyl,alkoxy, oxo, amino or alkylamino groups. Illustrative examples of thesubstituted alkyl groups are given below.

A pair of R¹⁰ and R¹¹, a pair of R¹⁰ and R¹², or a pair of R¹¹ and R¹²,taken together, may form a ring. Each of R¹⁰, R¹¹ and R¹² is a straightor branched alkylene group of 1 to 18 carbon atoms, preferably 1 to 10carbon atoms, when they form a ring.

R¹³ is a tertiary alkyl group of 4 to 20 carbon atoms, preferably 4 to15 carbon atoms, a trialkylsilyl group whose alkyl groups each have 1 to6 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms or a group offormula (4). Exemplary tertiary alkyl groups are tert-butyl, tert-amyl,1,1-diethylpropyl, 1-ethylcyclopentyl, 1-butylcyclopentyl,1-ethylcyclohexyl, 1-butylcyclohexyl, 1-ethyl-2-cyclopentenyl,1-ethyl-2-cyclohexenyl, and 2-methyl-2-adamantyl. Exemplarytrialkylsilyl groups are trimethylsilyl, triethylsilyl, anddimethyl-tert-butylsilyl. Exemplary oxoalkyl groups are 3-oxocyclohexyl,4-methyl-2-oxooxan-4-yl, and 5-methyl-2-oxooxoran-5-yl. Letter z is aninteger of 0 to 6.

R¹⁴ is a straight, branched or cyclic alkyl group of 1 to 8 carbon atomsor substituted or unsubstituted aryl group of 6 to 20 carbon atoms.Exemplary straight, branched or cyclic alkyl groups include methyl,ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl,n-pentyl, n-hexyl, cyclopentyl, cyclohexyl, cyclopentylmethyl,cyclopentylethyl, cyclohexylmethyl and cyclohexylethyl. Exemplarysubstituted or unsubstituted aryl groups include phenyl, methylphenyl,naphthyl, anthryl, phenanthryl, and pyrenyl. Letter h′ is equal to 0 or1, i is equal to 0, 1, 2 or 3, satisfying 2h′+i=2 or 3.

R¹⁵ is a straight, branched or cyclic alkyl group of 1 to 8 carbon atomsor substituted or unsubstituted aryl group of 6 to 20 carbon atoms,examples of which are as exemplified for R¹⁴. R¹⁶ to R²⁵ areindependently hydrogen or monovalent hydrocarbon groups of 1 to 15carbon atoms which may contain a hetero atom, for example, straight,branched or cyclic alkyl groups such as methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl,n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl, cyclopentylmethyl,cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl,and cyclohexylbutyl, and substituted ones of these groups in which somehydrogen atoms are replaced by hydroxyl, alkoxy, carboxy,alkoxycarbonyl, oxo, amino, alkylamino, cyano, mercapto, alkylthio, andsulfo groups. R¹⁶ to R²⁵, for example, a pair of R¹⁶ and R¹¹, a pair ofR¹⁶ and R¹⁸, a pair of R¹⁷ and R¹⁹, a pair of R¹⁸ and R¹⁹, a pair of R²⁰and R²¹, or a pair of R²² and R²³, taken together, may form a ring. WhenR¹⁶ to R²⁵ form a ring, they are divalent hydrocarbon groups which maycontain a hetero atom, examples of which are the above-exemplifiedmonovalent hydrocarbon groups with one hydrogen atom eliminated. Also,two of R¹⁶ to R²⁵ which are attached to adjacent carbon atoms (forexample, a pair of R¹⁶ and R¹⁸, a pair of R¹⁸ and R²⁴, or a pair of R²²and R²⁴) may directly bond together to form a double bond.

Of the acid labile groups of formula (4), illustrative examples of thestraight or branched groups are given below.

Of the acid labile groups of formula (4), illustrative examples of thecyclic groups include tetrahydrofuran-2-yl,2-methyltetrahydrofuran-2-yl, tetrahydropyran-2-yl and2-methyltetrahydropyran-2-yl.

Illustrative examples of the acid labile groups of formula (5) includetert-butoxycarbonyl, tert-butoxy-carbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonyl-methyl, 1,1-diethylpropyloxycarbonyl,1,1-diethylpropyloxycarbonylmethyl, 1-ethylcyclopentyl-oxycarbonyl,1-ethylcyclopentyloxycarbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyl-oxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl.

Illustrative examples of the acid labile groups of formula (6) include1-methylcyclopentyl, 1-ethylcyclopentyl, 1-n-propylcyclopentyl,1-isopropylcyclopentyl, 1-n-butylcyclopentyl, 1-sec-butylcyclopentyl,1-methylcyclohexyl, 1-ethylcyclohexyl, 3-methyl-1-cyclopenten-3-yl,3-ethyl-1-cyclopenten-3-yl, 3-methyl-1-cyclohexen-3-yl, and3-ethyl-1-cyclohexen-3-yl.

Illustrative examples of the acid labile groups of formula (7) are givenbelow.

Exemplary of the non-cyclic tertiary alkyl group of 4 to 20 carbonatoms, preferably 4 to 15 carbon atoms, are tert-butyl, tert-amyl,3-ethyl-3-pentyl and dimethylbenzyl.

Exemplary of the trialkylsilyl groups whose alkyl groups each have 1 to6 carbon atoms are trimethylsilyl, triethylsilyl, andtert-butyldimethylsilyl.

Exemplary of the oxoalkyl groups of 4 to 20 carbon atoms are3-oxocyclohexyl and groups represented by the following formulae.

Exemplary of the aryl-substituted alkyl groups of 7 to 20 carbon atomsare benzyl, methylbenzyl, dimethylbenzyl, diphenylmethyl, and1,1-diphenylethyl.

The onium salts according to the invention are salts ofsulfonyloxybenzenesulfonate anions with iodonium or sulfonium cations.Exemplary anions include a4-(4′-methylphenylsulfonyloxy)benzenesulfonate anion,4-(4′-methoxyphenylsulfonyloxy)benzenesulfonate anion,4-phenylsulfonyloxybenzenesulfonate anion,4-(2′,4′,6′-trimethylphenylsulfonyloxy)benzenesulfonate anion,4-(2′-naphthylsulfonyloxy)benzenesulfonate anion,4-((10′-camphorsulfonyloxy)benzenesulfonate anion,4-methanesulfonyloxybenzenesulfonate anion,4-(n-butanesulfonyloxy)benzenesulfonate anion,2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate anion, and2,5-bis(phenylsulfonyloxy)benzenesulfonate anion. Of these, preferredanions are 4-(4′-methylphenylsulfonyloxy)benzenesulfonate,4-phenylsulfonyloxybenzenesulfonate,4-(10′-camphorsulfonyloxy)benzenesulfonate,2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate, and2,5-bis(phenylsulfonyloxy)benzenesulfonate anions, and(4′-methylphenylsulfonyloxy)-methylbenzenesulfonate anions in which theposition of the substituents is not limited.

Exemplary iodonium cations include diphenyliodonium,bis(4-tert-butylphenyl)iodonium, 4-methoxyphenylphenyliodonium,4-ethoxyphenylphenyliodonium, and 4-tertbutoxyphenylphenyliodonium, withthe diphenyliodonium and bis(4-tert-butylphenyl)iodonium are preferred.

Exemplary sulfonium cations include triphenylsulfonium,4-hydroxyphenyldiphenylsulfonium, (4-tert-butylphenyl)diphenylsulfonium,bis(4-tert-butylphenyl)phenylsulfonium,tris(4-tert-butylphenyl)sulfonium, 4-methylphenyldiphenylsulfonium,bis(4-methylphenyl)phenylsulfonium, tris(4-methylphenyl)sulfonium,(4-tert-butoxyphenyl)diphenylsulfonium,bis(4-tert-butoxyphenyl)phenylsulfonium,tris(4-tert-butoxyphenyl)sulfonium,(3-tert-butoxyphenyl)diphenylsulfonium,bis(3-tert-butoxyphenyl)phenylsulfonium,tris(3-tert-butoxyphenyl)-sulfonium,(3,4-di-tert-butoxyphenyl)diphenylsulfonium,bis(3,4-di-tert-butoxyphenyl)phenylsulfonium,tris(3,4-di-tert-butoxyphenyl)sulfonium,diphenyl(4-thiophenoxyphenyl)sulfonium,(4-tert-butoxycarbonylmethyloxyphenyl)diphenylsulfonium,tris(4-tert-butoxycarbonylmethyloxyphenyl)sulfonium,(4-tert-butoxyphenyl)bis(4-dimethylaminophenyl)sulfonium,tris(4-methoxyphenyl)sulfonium, tris(4-ethoxyphenyl)sulfonium,tris(4-dimethylaminophenyl)sulfonium, 2-naphthyldiphenylsulfonium,dimethyl-2-naphthylsulfonium, 4-hydroxyphenyldimethylsulfonium,4-methoxyphenyldimethylsulfonium, dimethylphenylsulfonium,diphenylmethylsulfonium, trimethylsulfonium,2-oxocyclohexylcyclohexylmethylsulfonium,2-oxocyclohexyl-methyl-phenylsulfonium,2-oxocyclopentyl-methyl-phenylsulfonium,2-oxopropyl-methyl-phenylsulfonium, and tribenzylsulfonium. Of these,preferred are triphenylsulfonium, 4-tert-butoxyphenyldiphenylsulfonium,diphenylmethylsulfonium, dimethylphenylsulfonium,4-tert-butylphenyldiphenylsulfonium, tris(4-methylphenyl)sulfonium, andtris(4-tert-butylphenyl)sulfonium.

Especially useful onium salts are:

triphenylsulfonium 4-(4′-methylphenylsulfonyloxy)benzene-sulfonate,

4-tert-butoxyphenyldiphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate,

4-tert-butylphenyldiphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate,

dimethylphenylsulfonium 4-(4′-methylphenylsulfonyloxy)benzenesulfonate,

tris(4-tert-butoxyphenyl)sulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate,

tris(4-methylphenyl)sulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate,

tris(4-tert-butylphenyl)sulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate,

triphenylsulfonium 4-(10′-camphorsulfonyloxy)benzenesulfonate,

4-tert-butoxyphenyldiphenylsulfonium4-(10′-camphorsulfonyloxy)benzenesulfonate,

4-tert-butylphenyldiphenylsulfonium4-(10′-camphorsulfonyloxy)benzenesulfonate,

dimethylphenylsulfonium 4-(10′-camphorsulfonyloxy)benzenesulfonate,

tris(4-tert-butoxyphenyl)sulfonium4-(10′-camphorsulfonyloxy)benzenesulfonate,

diphenyliodonium 4-(4′-methylphenylsulfonyloxy)benzenesulfonate,

bis(4-tert-butylphenyl)iodonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate,

bis(4-tert-butylphenyl)iodonium4-(10′-camphorsulfonyloxy)benzenesulfonate,

triphenylsulfonium 2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate,

tris(4-methylphenyl)sulfonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate,

tris(4-tert-butylphenyl)sulfonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate, and

bis(4-tert-butylphenyl)iodonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate.

The onium salts can be synthesized by the following method although thesynthesis method is not limited thereto.

The sulfonyloxybenzenesulfonate anion of the onium salt according to theinvention may be obtained either by condensing a phenolic hydroxylgroup-containing benzenesulfonic acid (e.g., phenolsulfonic acid,hydroquinonesulfonic acid or cresolsulfonic acid) with a sulfonyl halideor sulfonic anhydride, or by sulfonating a sulfonic acid phenol ester.In the process of condensing a phenolic hydroxyl group-containingbenzenesulfonic acid with a sulfonyl halide, reaction should be effectedunder basic conditions.

Herein, R¹, R², p and q are as defined above.

Also in condensing a phenol with a sulfonyl chloride, reaction ispreferably effected under basic conditions. The sulfonating process maybe effected in a conventional manner using sulfur trioxide, sulfuricacid, chlorosulfonic acid or amidosulfuric acid.

Herein, R¹, R², p and q are as defined above.

The process for the synthesis of corresponding sulfonium and iodoniumsalts is not critical although the preferred anions are halide ions andalkylsulfonic acid anions (alkyl sulfonate) having a lower acid strengththan arylsulfonic acids. It is noted that a sulfonium salt having astrong acid anion such as trifluoromethanesulfonic acid anion isdifficult to effect anion exchange with the above-synthesizedsulfonyloxybenzenesulfonic acid. When an onium salt having a strong acidanion is used as a starting reactant, it is desirable to first effectanion exchange using an ion-exchange chromatogram as described in JP-A7-333844, obtaining an onium salt having a hydroxide ion, followed byfurther anion exchange with the above sulfonyloxybenzenesulfonic acidanion. The sulfonium and iodonium salts can be synthesized according tothe teachings of The Chemistry of Sulfonium Group, Part 1, John-Wiley &Sons (1981), Advanced Photochemistry, vol. 17, John-Wiley & Sons (1992),J. Org. Chem., 1988, 53, 5571-5573, and JP-A 7-25846.

The anion exchange is desirably effected using at least 1 mol and moredesirably 1 to 3 mol of the above-synthesized sulfonyloxybenzenesulfonicacid anion per mol of the onium salt, though the reaction conditions arenot limited thereto. The solvent system may be an alcoholic solvent suchas methanol or ethanol or a two layer system such as adichloromethane/water mixture. For anion exchange of onium salts havinga halide ion, the use of lead carbonate as described in JP-A 9-323970ensures more quantitative exchange.

The onium salts of formulae (1), (1a), (1a′) and (1b) find best use asthe photoacid generator in resist materials, especially chemicalamplification type resist materials although the application of theonium salts is not limited thereto.

Resist Composition

The onium salts of formulae (1), (1a), (1a′) and (1b) are useful as thephotoacid generator in resist materials sensitive to radiation such asultraviolet, deep ultraviolet, electron beams, x-rays, excimer laser,y-rays, and synchrotron radiation for use in the microfabrication ofintegrated circuits, especially in chemical amplification type resistcompositions. The resist compositions may be either positive or negativeworking although they are preferably of the chemical amplification type.

The invention provides the following resist compositions:

(i) a resist composition comprising an onium salt of formula (1) as aphotoacid generator;

(ii) a resist composition comprising a sulfonium salt of formula (1a) asa photoacid generator;

(iii) a resist composition comprising a sulfonium salt of formula (1a′)as a photoacid generator; and

(iv) a resist composition comprising a iodonium salt of formula (1b) asa photoacid generator.

The resist compositions of the invention include a variety ofembodiments,

1) a chemically amplified positive working resist composition comprising(A) a resin which changes its solubility in an alkaline developer underthe action of an acid, (B) an onium salt of formula (1), (1a), (1a′) or(1b), and (J) an organic solvent;

2) a chemically amplified positive working resist composition of 1)further comprising (C) a photoacid generator capable of generating anacid upon exposure to radiation other than component (B);

3) a chemically amplified positive working resist composition of 1) or2) further comprising (F) a compound with a molecular weight of up to3,000 which changes its solubility in an alkaline developer under theaction of an acid;

4) a chemically amplified positive working resist composition of 1) to3) further comprising (G) a basic compound;

5) a chemically amplified positive working resist composition of 1) to4) further comprising (E) an organic acid derivative;

6) a chemically amplified negative working resist composition comprising(B) an onium salt of formula (1), (1a), (1a′) or (1b) capable ofgenerating an acid upon, exposure to radiation, (H) an alkali-solubleresin, (I) an acid crosslinking agent capable of forming a crosslinkedstructure under the action of an acid, and (J) an organic solvent;

7) a chemically amplified negative working resist composition of 6)further comprising (C) another photoacid generator; and

8) a chemically amplified negative working resist composition of 6) or7) further comprising (F) a compound with a molecular weight of up to3,000 which changes its solubility in an alkaline developer under theaction of an acid; but not limited thereto.

Referring to the resin (A), the following resins are preferred.

(A-i) A resin having such substituent groups having C—O—C linkages thatthe solubility in an alkaline developer changes as a result of cleavageof the C—O—C linkages under the action of an acid.

(A-ii) A polymer containing phenolic hydroxyl groups in which hydrogenatoms of the phenolic hydroxyl groups are substituted by acid labilegroups of at least one type in a proportion of more than 0 mol % to 80mol %, on the average, of the entire hydrogen atoms of the phenolichydroxyl groups, the polymer having a weight average molecular weight of3,000 to 100,000.

(A-iii) A polymer comprising recurring units represented by thefollowing general formula (2):

wherein R⁴ is hydrogen or methyl, R⁵ is a straight, branched or cyclicalkyl group of 1 to 8 carbon atoms, x is 0 or a positive integer, y is apositive integer, and x+y is up to 5, in which hydrogen atoms of thephenolic hydroxyl groups are substituted by acid labile groups of atleast one type in a proportion of more than 0 mol % to 80 mol %, on theaverage, of the entire hydrogen atoms of the phenolic hydroxyl groups,the polymer having a weight average molecular weight of 3,000 to100,000.

(A-iv) A polymer of formula (2) in which some of the hydrogen atoms ofthe phenolic hydroxyl groups are replaced by acid labile groups of atleast one type, and the hydrogen atoms of the remaining phenolichydroxyl groups are crosslinked within a molecule and/or betweenmolecules, in a proportion of more than 0 mol % to 50 mol %, on theaverage, of the entire phenolic hydroxyl groups on the polymer, withcrosslinking groups having C—O—C linkages represented by the followinggeneral formula (3a) or (3b):

wherein each of R⁷ and R⁸ is hydrogen or a straight, branched or cyclicalkyl group of 1 to 8 carbon atoms, or R⁷ and R⁸, taken together, mayform a ring, and each of R⁷ and R⁸ is a straight or branched alkylenegroup of 1 to 8 carbon atoms when they form a ring, R⁹ is a straight,branched or cyclic alkylene group of 1 to 10 carbon atoms, letter a′ isan integer of 1 to 7, letter b is 0 or an integer of 1 to 10, A is an(a′+1)-valent aliphatic or alicyclic saturated hydrocarbon group,aromatic hydrocarbon group or heterocyclic group of 1 to 50 carbonatoms, which may be separated by a hetero atom and in which some of thehydrogen atoms attached to carbon atoms may be replaced by hydroxyl,carboxyl, carbonyl or halogen, B is —CO—O—, —NHCO—O— or —NHCONH—.

(A-v) A polymer comprising recurring units represented by the followinggeneral formula (2a′):

wherein R⁴ is hydrogen or methyl, R⁵ is a straight, branched or cyclicalkyl group of 1 to 8 carbon atoms, R⁶ is an acid labile group, R^(6a)is hydrogen or an acid labile group, R^(6a) being at least partially anacid labile group, x is 0 or a positive integer, y is a positiveinteger, satisfying x+y≦5, the R⁶ groups may be the same or differentwhen y is 2 or more, M and N are positive integers, L is 0 or a positiveinteger, satisfying 0<N/(M+N)≦0.5 and 0<(N+L)/(M+N+L)≦0.8, wherein theunits of acrylate and methacrylate are contained in the polymer in aproportion of more than 0 mol % to 50 mol % on the average, the acidlabile groups are present in a proportion of more than 0 mol % to 80 mol%, on the average, based on the entire polymer, and the polymer has aweight average molecular weight of 3,000 to 100,000.

Preferably the acid labile groups are groups of the following generalformulae (4) to (7), non-cyclic tertiary alkyl groups of 4 to 20 carbonatoms, trialkylsilyl groups whose alkyl groups each have 1 to 6 carbonatoms, oxoalkyl groups of 4 to 20 carbon atoms, or aryl-substitutedalkyl groups of 7 to 20 carbon atoms.

Herein

R¹⁰ and R¹¹ are independently hydrogen or straight, branched or cyclicalkyl groups of 1 to 18 carbon atoms, R¹² is a monovalent hydrocarbongroup of 1 to 18 carbon atoms which may have a hetero atom, or R¹⁰ andR¹¹, R¹⁰ and R¹², or R¹¹ and R¹², taken together, may form a ring, withthe proviso that each of R¹⁰, R¹¹ and R¹² is a straight or branchedalkylene group of 1 to 18 carbon atoms when they form a ring,

R¹³ is a tertiary alkyl group of 4 to 20 carbon atoms, a trialkylsilylgroup whose alkyl groups each have 1 to 6 carbon atoms, an oxoalkylgroup of 4 to 20 carbon atoms or a group of formula (4), and letter z isan integer of 0 to 6,

R¹⁴ is a straight, branched or cyclic alkyl group of 1 to 8 carbon atomsor substituted or unsubstituted aryl group of 6 to 20 carbon atoms, h′is equal to 0 or 1, i is equal to 0, 1, 2 or 3, satisfying 2h′+i=2 or 3,

R¹⁵ is a straight, branched or cyclic alkyl group of 1 to 8 carbon atomsor substituted or unsubstituted aryl group of 6 to 20 carbon atoms, R¹⁶to R²⁵ are independently hydrogen or monovalent hydrocarbon groups of 1to 15 carbon atoms which may contain a hetero atom, or R¹⁶ to R²⁵, takentogether, may form a ring, with the proviso that they are divalenthydrocarbon groups of 1 to 15 carbon atoms which may contain a heteroatom when they form a ring, or two of R¹⁶ to R²⁵ which are attached toadjacent carbon atoms may directly bond together to form a double bond.

Moreover, the invention provides a process for forming a pattern,comprising the steps of applying the resist composition defined aboveonto a substrate to form a coating; heat treating the coating andexposing the coating to high energy radiation with a wavelength of up to300 nm or electron beam through a photo-mask; optionally heat treatingthe exposed coating, and developing the coating with a developer.

Now the respective components of the resist composition are described indetail.

Component (J)

Component (J) is an organic solvent. Illustrative, non-limiting,examples include butyl acetate, amyl acetate, cyclohexyl acetate,3-methoxybutyl acetate, methyl ethyl ketone, methyl amyl ketone,cyclohexanone, cyclopentanone, 3-ethoxyethyl propionate, 3-ethoxymethylpropionate, 3-methoxymethyl propionate, methyl acetoacetate, ethylacetoacetate, diacetone alcohol, methyl pyruvate, ethyl pyruvate,propylene glycol monomethyl ether, propylene glycol monoethyl ether,propylene glycol monomethyl ether propionate, propylene glycol monoethylether propionate, ethylene glycol monomethyl ether, ethylene glycolmonoethyl ether, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, 3-methyl-3-methoxybutanol, N-methylpyrrolidone,dimethylsulfoxide, γ-butyrolactone, propylene glycol methyl etheracetate, propylene glycol ethyl ether acetate, propylene glycol propylether acetate, methyl lactate, ethyl lactate, propyl lactate, andtetramethylene sulfone. Of these, the propylene glycol alkyl etheracetates and alkyl lactates are especially preferred.

It is noted that the alkyl groups of the propylene glycol alkyl etheracetates are preferably those of 1 to 4 carbon atoms, for example,methyl, ethyl and propyl, with methyl and ethyl being especiallypreferred. Since the propylene glycol alkyl ether acetates include 1,2-and 1,3-substituted ones, each includes three isomers depending on thecombination of substituted positions, which may be used alone or inadmixture. It is also noted that the alkyl groups of the alkyl lactatesare preferably those of 1 to 4 carbon atoms, for example, methyl, ethyland propyl, with methyl and ethyl being especially preferred. Thesesolvents may be used alone or in admixture. An exemplary useful solventmixture is a mixture of a propylene glycol alkyl ether acetate and analkyl lactate. The mixing ratio of the propylene glycol alkyl etheracetate and the alkyl lactate is not critical although it is preferredto mix 50 to 99 parts by weight of the propylene glycol alkyl etheracetate with 50 to 1 parts by weight of the alkyl lactate. It is morepreferred to mix 60 to 95% by weight of the propylene glycol alkyl etheracetate with 40 to 5% by weight of the alkyl lactate. A lower proportionof the propylene glycol alkyl ether acetate would invite a problem ofinefficient coating whereas a higher proportion thereof would provideinsufficient dissolution and allow for particle and defect formation. Alower proportion of the alkyl lactate would provide insufficientdissolution and cause the problem of many particles and defect whereas ahigher proportion thereof would lead to a composition which has a toohigh viscosity to apply and loses storage stability. The solvent mixtureof the propylene glycol alkyl ether acetate and the alkyl lactate mayfurther contain one or more other solvents.

Component (A)

Component (A) is a resin which changes its solubility in an alkalinedeveloper solution under the action of an acid. It is preferably, thoughnot limited thereto, an alkali-soluble resin having phenolic hydroxyland/or carboxyl groups in which some or all of the phenolic hydroxyland/or carboxyl groups are protected with acid-labile protective groupsrepresented by C—O—C linkages.

The alkali-soluble resins having phenolic hydroxyl and/or carboxylgroups include homopolymers and copolymers of p-hydroxystyrene,m-hydroxystyrene, α-methyl-p-hydroxystyrene, 4-hydroxy-2-methylstyrene,4-hydroxy-3-methylstyrene, methacrylic acid and acrylic acid, and suchcopolymers having a carboxylic derivative or diphenyl ethyleneintroduced at their terminus.

Also included are copolymers in which units free of alkali-soluble sitessuch as styrene, α-methylstyrene, acrylate, methacrylate, hydrogenatedhydroxystyrene, maleic anhydride and maleimide are introduced inaddition to the above-described units in such a proportion that thesolubility in an alkaline developer may not be extremely reduced.Substituents on the acrylates and methacrylates may be any of thesubstituents which do not undergo acidolysis. Exemplary substituents arestraight, branched or cyclic C₁₋₈ alkyl groups and aromatic groups suchas aryl groups, but not limited thereto.

Examples of the alkali-soluble resins are given below. These polymersmay also be used as the material from which the resin (A) which changesits solubility in an alkaline developer under the action of an acid isprepared and as the alkali-soluble resin which serves as component (H)to be described later. Examples include poly(p-hydroxystyrene),poly(m-hydroxystyrene), poly(4-hydroxy-2-methylstyrene),poly(4-hydroxy-3-methylstyrene), poly(α-methyl-p-hydroxystyrene),partially hydrogenated p-hydroxystyrene copolymers,p-hydroxystyrene-α-methyl-p-hydroxystyrene copolymers,p-hydroxystyrene-α-methylstyrene copolymers, p-hydroxystyrene-styrenecopolymers, p-hydroxystyrene-m-hydroxystyrene copolymers,p-hydroxystyrene-styrene copolymers, p-hydroxystyrene-acrylic acidcopolymers, p-hydroxystyrene-methacrylic acid copolymers,p-hydroxystyrene-methyl methacrylate copolymers,p-hydroxystyrene-acrylic acid-methyl methacrylate copolymers,p-hydroxystyrene-methyl acrylate copolymers,p-hydroxystyrene-methacrylic acid-methyl methacrylate copolymers,poly(methacrylic acid), poly(acrylic acid), acrylic acid-methyl acrylatecopolymers, methacrylic acid-methyl methacrylate copolymers, acrylicacid-maleimide copolymers, methacrylic acid-maleimide copolymers,p-hydroxystyreneacrylic acid-maleimide copolymers, andp-hydroxystyrenemethacrylic acid-maleimide copolymers, but are notlimited to these combinations.

Preferred are poly(p-hydroxystyrene), partially hydrogenatedp-hydroxystyrene copolymers, p-hydroxystyrene-styrene copolymers,p-hydroxystyrene-acrylic acid copolymers, andp-hydroxystyrene-methacrylic acid copolymers.

Alkali-soluble resins comprising units of the following formula (2) or(2′) are especially preferred.

Herein R⁴ is hydrogen or methyl, R⁵ is a straight, branched or cyclicalkyl group of 1 to 8 carbon atoms, x is 0 or a positive integer, y is apositive integer, satisfying x+y≦5, and M and N are positive integers,satisfying 0<N/(M+N)≦0.5.

The polymer should preferably have a weight average molecular weight(Mw) of 3,000 to 100,000. Many polymers with Mw of less than 3,000 donot perform well and are poor in heat resistance and film formation.Many polymers with Mw of more than 100,000 give rise to a problem withrespect to dissolution in the resist solvent and developer. The polymershould also preferably have a dispersity (Mw/Mn) of up to 3.5, and morepreferably up to 1.5. With a dispersity of more than 3.5, resolution islow in many cases. Although the preparation method is not critical, apoly(p-hydroxystyrene) or similar polymer with a low dispersity ornarrow dispersion can be synthesized by living anion polymerization.

In the resist composition using an onium salt of formula (1), (1a),(1a′) or (1b), a resin having such substituent groups with C—O—Clinkages (acid labile groups) that the solubility in an alkalinedeveloper changes as a result of severing of the C—O—C linkages underthe action of an acid, especially an alkali-soluble resin as mentionedabove is preferably used as component (A). Especially preferred is apolymer comprising recurring units of the above formula (2) andcontaining phenolic hydroxyl groups in which hydrogen atoms of thephenolic hydroxyl group are replaced by acid labile groups of one ormore types in a proportion of more than 0 mol % to 80 mol % on theaverage of the entire hydrogen atoms of the phenolic hydroxyl group, thepolymer having a weight average molecular weight of 3,000 to 100,000.

Also preferred is a polymer comprising recurring units of the aboveformula (2′), that is, a copolymer comprising p-hydroxystyrene and/orα-methyl-p-hydroxystyrene and acrylic acid and/or methacrylic acid,wherein some of the hydrogen atoms of carboxyl groups of the acrylicacid and/or methacrylic acid are replaced by acid labile groups of oneor more types to form an ester, the units based on the acrylic esterand/or methacrylic ester are contained in a proportion of more than 0mol % to 50 mol %, on the average, of the copolymer, and wherein some ofthe hydrogen atoms of the phenolic hydroxyl groups of p-hydroxystyreneand/or α-methyl-p-hydroxystyrene may be replaced by acid labile groupsof one or more types. Further preferred is such a copolymer in which theunits based on the acrylic ester and/or methacrylic ester and thep-hydroxystyrene and/or α-methyl-p-hydroxystyrene having acid labilegroups substituted thereon are contained in a proportion of more than 0mol % to 80 mol %, on the average, of the copolymer.

Exemplary such polymers are polymers comprising recurring unitsrepresented by the following general formula (2a) or (2a′) and having aweight average molecular weight of 3,000 to 100,000.

Herein, R⁴ is hydrogen or methyl. R⁵ is a straight, branched or cyclicalkyl group of 1 to 8 carbon atoms. R⁶ is an acid labile group. R^(6a)is hydrogen or an acid labile group, at least some, preferably all ofthe R^(6a) groups are acid labile groups. Letter x is 0 or a positiveinteger, and y is a positive integer, satisfying x+y≦5. The R⁶ groupsmay be the same or different when y is 2 or more. S and T are positiveintegers, satisfying 0<S/(S+T)≦0.8. M and N are positive integers, L is0 or a positive integer, satisfying 0<N/(M+N)≦0.5 and0<(N+L)/(M+N+L)<0.8.

R⁵ stands for straight, branched or cyclic C₁₋₈ alkyl groups, forexample, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl,tert-butyl, cyclohexyl and cyclopentyl.

With respect to the acid labile groups, where some of the phenolichydroxyl groups and some or all of the carboxyl groups in thealkali-soluble resin are protected with acid labile groups having C—O—Clinkages, the acid labile groups are selected from a variety of suchgroups. The preferred acid labile groups are groups of the followinggeneral formulae (4) to (7), non-cyclic tertiary alkyl group of 4 to 20carbon atoms, preferably 4 to 15 carbon atoms, trialkylsilyl groupswhose alkyl groups each have 1 to 6 carbon atoms, oxoalkyl groups of 4to 20 carbon atoms, or aryl-substituted alkyl groups of 7 to 20 carbonatoms.

Herein R¹⁰ and R¹¹ are independently hydrogen or straight, branched orcyclic alkyl groups of 1 to 18 carbon atoms, preferably 1 to 10 carbonatoms, for example, methyl, ethyl, propyl, isopropyl, n-butyl,sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl andn-octyl. R¹² is a monovalent hydrocarbon group of 1 to 18 carbon atoms,preferably 1 to 10 carbon atoms, which may have a hetero atom (e.g.,oxygen atom), for example, straight, branched or cyclic alkyl groups,and such groups in which some hydrogen atoms are replaced by hydroxyl,alkoxy, oxo, amino or alkylamino groups. Illustrative examples of thesubstituted alkyl groups are given below.

A pair of R¹⁰ and R¹¹, a pair of R¹⁰ and R¹², or a pair of R¹¹ and R¹²,taken together, may form a ring. Each of R¹⁰, R¹¹ and R¹² is a straightor branched alkylene group of 1 to 18 carbon atoms, preferably 1 to 10carbon atoms, when they form a ring.

R¹³ is a tertiary alkyl group of 4 to 20 carbon atoms, preferably 4 to15 carbon atoms, a trialkylsilyl group whose alkyl groups each have 1 to6 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms or a group offormula (4). Exemplary tertiary alkyl groups are tert-butyl, tert-amyl,1,1-diethylpropyl, 1-methylcyclopentyl, 1-ethylcyclopentyl,1-isopropylcyclopentyl, 1-butylcyclopentyl, 1-methylcyclohexyl,1-ethylcyclohexyl, 1-isopropylcyclohexyl, 1-butylcyclohexyl,1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and2-methyl-2-adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl,triethylsilyl, and dimethyl-tert-butylsilyl. Exemplary oxoalkyl groupsare 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and5-methyl-2-oxooxoran-5-yl. Letter z is an integer of 0 to 6.

R¹⁴ is a straight, branched or cyclic alkyl group of 1 to 8 carbon atomsor substituted or unsubstituted aryl group of 6 to 20 carbon atoms.Exemplary straight, branched or cyclic alkyl groups include methyl,ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl,n-pentyl, n-hexyl, cyclopentyl, cyclohexyl, cyclopentylmethyl,cyclopentylethyl, cyclohexylmethyl and cyclohexylethyl. Exemplarysubstituted or unsubstituted aryl groups include phenyl, methylphenyl,naphthyl, anthryl, phenanthryl, and pyrenyl. Letter h′ is equal to 0 or1, i is equal to 0, 1, 2 or 3, satisfying 2h′+i=2 or 3.

R¹⁵ is a straight, branched or cyclic alkyl group of 1 to 8 carbon atomsor substituted or unsubstituted aryl group of 6 to 20 carbon atoms,examples of which are as exemplified for R¹⁴. R¹⁶ to R²⁵ areindependently hydrogen or monovalent hydrocarbon groups of 1 to 15carbon atoms which may contain a hetero atom, for example, straight,branched or cyclic alkyl groups such as methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl,n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl, cyclopentylmethyl,cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl,and cyclohexylbutyl, and substituted ones of these groups in which somehydrogen atoms are replaced by hydroxyl, alkoxy, carboxy,alkoxycarbonyl, oxo, amino, alkylamino, cyano, mercapto, alkylthio, andsulfo groups. R¹⁶ to R²⁵, for example, a pair of R¹⁶ and R¹⁷ , a pair ofR¹⁶ and R¹⁸, a pair of R¹⁷ and R¹⁹, a pair of R¹⁸ and R¹⁹, a pair of R²⁰and R²¹, or a pair of R²² and R²³, taken together, may form a ring. WhenR¹⁶ to R²⁵ form a ring, they are divalent C₁₋₁₅ hydrocarbon groups whichmay contain a hetero atom, examples of which are the above-exemplifiedmonovalent hydrocarbon groups with one hydrogen atom eliminated. Also,two of R¹⁶ to R²⁵ which are attached to adjacent carbon atoms (forexample, a pair of R¹⁶ and R¹⁸, a pair of R¹⁸ and R²⁴, or a pair of R²²and R²⁴) may directly bond together to form a double bond.

Of the acid labile groups of formula (4), illustrative examples of thestraight or branched groups are given below.

Of the acid labile groups of formula (4), illustrative examples of thecyclic groups include tetrahydrofuran-2-yl,2-methyltetrahydrofuran-2-yl, tetrahydropyran-2-yl and2-methyltetrahydropyran-2-yl.

Illustrative examples of the acid labile groups of formula (5) includetert-butoxycarbonyl, tert-butoxycarbonylmethyl, tert-amyloxycarbonyl,tert-amyloxycarbonylmethyl, 1,1-diethylpropyloxycarbonyl,1,1-diethylpropyloxycarbonylmethyl, 1-ethylcyclopentyloxycarbonyl,1-ethylcyclopentyloxycarbonylmethyl, 1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl.

Illustrative examples of the acid labile groups of formula (6) include1-methylcyclopentyl, 1-ethylcyclopentyl, 1-n-propylcyclopentyl,1-isopropylcyclopentyl, 1-n-butylcyclopentyl, 1-sec-butylcyclopentyl,1-methylcyclohexyl, 1-ethylcyclohexyl, 3-methyl-1-cyclopenten-3-yl,3-ethyl-1-cyclopenten-3-yl, 3-methyl-1-cyclohexen-3-yl, and3-ethyl-1-cyclohexen-3-yl.

Illustrative examples of the acid labile groups of formula (7) are givenbelow.

Exemplary of the non-cyclic tertiary alkyl group of 4 to 20 carbonatoms, preferably 4 to 15 carbon atoms, are tert-butyl, tert-amyl,3-ethyl-3-pentyl and dimethylbenzyl.

Exemplary of the trialkylsilyl groups whose alkyl groups each have 1 to6 carbon atoms are trimethylsilyl, triethylsilyl, andtert-butyldimethylsilyl.

Exemplary of the oxoalkyl groups of 4 to 20 carbon atoms are3-oxocyclohexyl and groups represented by the following formulae.

Exemplary of the aryl-substituted alkyl groups of 7 to 20 carbon atomsare benzyl, methylbenzyl, dimethylbenzyl, diphenylmethyl, and1,1-diphenylethyl.

In the resist composition comprising an onium salt of formula (1), (1a),(1a′) or (1b), the resin (A) may be the polymer of formula (2) or (2′)in which some of the hydrogen atoms of the phenolic hydroxyl groups arereplaced by acid labile groups of one or more types, and the hydrogenatoms of the remaining phenolic hydroxyl groups are crosslinked within amolecule and/or between molecules, in a proportion of more than 0 mol %to 50 mol %, on the average, of the entire phenolic hydroxyl groups onthe polymer, with crosslinking groups having C—O—C linkages representedby the following general formula (3a) or (3b).

The crosslinking groups having C—O—C linkages are groups represented bythe following general formula (3a) or (3b), preferably the followinggeneral formula (3a′) or (3b′).

Herein, each of R⁷ and R⁸ is hydrogen or a straight, branched or cyclicalkyl group of 1 to 8 carbon atoms, or R⁷ and R⁸, taken together, mayform a ring, and each of R⁷ and R⁸ is a straight or branched alkylenegroup of 1 to 8 carbon atoms when they form a ring. R⁹ is a straight,branched or cyclic alkylene group of 1 to 10 carbon atoms, letter a′ isan integer of 1 to 7, letter b is 0 or an integer of 1 to 10. A is an(a′+1)-valent aliphatic or alicyclic saturated hydrocarbon group,aromatic hydrocarbon group or heterocyclic group of 1 to 50 carbonatoms, which may be separated by a hetero atom and in which some of thehydrogen atoms attached to carbon atoms may be replaced by hydroxyl,carboxyl, carbonyl or halogen. B is —CO—O—, —NHCO—O— or —NHCONH—.

Herein, each of R⁷ and R⁸ is hydrogen or a straight, branched or cyclicalkyl group of 1 to 8 carbon atoms, or R⁷ and R⁸, taken together, mayform a ring, and each of R⁷ and R⁸ is a straight or branched alkylenegroup of 1 to 8 carbon atoms when they form a ring. R⁹ is a straight,branched or cyclic alkylene group of 1 to 10 carbon atoms, letter a′″ isan integer of 1 to 3, letter b is 0 or an integer of 1 to 5. A is an(a″′1+1)-valent straight, branched or cyclic alkylene, alkyltriyl oralkyltetrayl group of 1 to 20 carbon atoms or arylene group of 6 to 30carbon atoms, which may be separated by a hetero atom and in which someof the hydrogen atoms attached to carbon atoms may be replaced byhydroxyl, carboxyl, acyl or halogen. B is —CO—O—, —NHCO—O— or —NHCONH—.

Examples of the straight, branched or cyclic C₁,₈ alkyl grouprepresented by R⁷ and R⁸ are as exemplified for R⁵.

Examples of the straight, branched or cyclic C₁₋₁₀ alkylene grouprepresented by R⁹ include methylene, ethylene, propylene, isopropylene,n-butylene, isobutylene, cyclohexylene, and cyclopentylene.

Exemplary halogen atoms are fluorine, chlorine, bromine and iodine.

Illustrative examples of A are described later. These crosslinkinggroups of formulae (3a) and (3b) originate from alkenyl ether compoundsand halogenated alkyl ether compounds to be described later. Asunderstood from the value of a′ in formula (3a) or (3b), thecrosslinking group is not limited to a divalent one and trivalent tooctavalent groups are acceptable. For example, the divalent crosslinkinggroup is exemplified by groups of the following formulas (3a″) and(3b″), and the trivalent crosslinking group is exemplified by groups ofthe following formulas (3a″′) and (3b″′).

In the resist composition of the invention, the preferred polymer is apolymer comprising recurring units of the following general formula (2b)or (2b′), and more preferably the same polymer in which hydrogen atomsof phenolic hydroxyl groups represented by R are eliminated to leaveoxygen atoms which are crosslinked within a molecule and/or betweenmolecules with crosslinking groups having C—O—C linkages represented bythe above formula (3a) or (3b).

Herein, R represents a crosslinking group, attached to an oxygen atom,represented by the above formula (3a) or (3b). R⁴ is hydrogen or methyl,R⁵ is a straight, branched or cyclic alkyl group of 1 to 8 carbon atoms.R¹⁰ and R¹¹ are independently hydrogen or straight, branched or cyclicalkyl groups of 1 to 18 carbon atoms, R¹² is a monovalent hydrocarbongroup of 1 to 18 carbon atoms which may have a hetero atom, or R¹⁰ andR¹¹, R¹⁰ and R₁₂, or R¹¹ and R¹², taken together, may form a ring, withthe proviso that each of R¹⁰, R¹¹ and R¹² is a straight or branchedalkylene group of 1 to 18 carbon atoms when they form a ring. R¹³ is atertiary alkyl group of 4 to 20 carbon atoms, an aryl-substituted alkylgroup of 7 to 20 carbon atoms, an oxoalkyl group of 4 to 20 carbon atomsor a group represented by —CR¹⁰R¹¹OR¹². Letter z is an integer of 0 to6. S2 is a positive number, each of S1, T1, and T2 is 0 or a positivenumber, satisfying 0≦S1/(S1+T1+T2+S2)≦0.8, 0≦T1/(S1+T1+T2+S2)≦0.8,0≦T2/(S1+T1+T2+S2)≦0.8, and S1+T1+T2+S2 =1. T1 and T2 are not equal to 0at the same time. Each of u and w is 0 or a positive integer, and v is apositive integer, satisfying u+v+w≦5. Letters x and y are as definedabove.

More preferably, S1, S2, T1 and T2 satisfy the following ranges.

0≦S1/(S1+T1+T2+S2)≦0.5,

especially 0.002≦S1/(S1+T1+T2+S2)≦0.2

0≦T1/(S1+T1+T2+S2)≦0.5,

especially 0≦T1/(S1+T1+T2+S2)≦0.4

0≦T2/(S1+T1+T2+S2)≦0.5,

especially 0≦T2/(S1+T1+T2+S2)≦0.4

0.4≦S2/(S1+T1+T2+S2)≦1,

especially 0.5≦S2/(S1+T1+T2+S2)≦0.9

0≦(T1+T2)/(S1+T1+T2+S2)≦0.5,

especially 0.1≦(T1+T2)/(S1+T1+T2+S2)≦0.4

It is also preferred that T1/(T1+T2) be from 0 to 1, more preferablyfrom 0.5 to 1, and most preferably from 0.7 to 1.

Herein, R represents a crosslinking group having C—O—C linkages,attached to an oxygen atom, represented by the above formula (3a) or(3b). R⁴is hydrogen or methyl, R⁵ is a straight, branched or cyclicalkyl group of 1 to 8 carbon atoms. R^(6a) is hydrogen or an acid labilegroup as mentioned above, and at least some, preferably all of theR^(6a) groups are acid labile groups. R¹⁰ and R¹¹ are independentlyhydrogen or straight, branched or cyclic alkyl groups of 1 to 18 carbonatoms, R¹² is a monovalent hydrocarbon group of 1 to 18 carbon atomswhich may have a hetero atom, or R¹⁰ and R¹¹, R¹⁰ and R¹², or R¹¹ andR¹², taken together, may form a ring, with the proviso that each of R¹⁰,R¹¹ and R¹² is a straight or branched alkylene group of 1 to 18 carbonatoms when they form a ring. R¹³ is a tertiary alkyl group of 4 to 20carbon atoms, an aryl-substituted alkyl group of 7 to 20 carbon atoms,an oxoalkyl group of 4 to 20 carbon atoms or a group represented by—CR¹⁰R¹¹OR¹². Letter z is an integer of 0 to 6. M2 is a positive number,each of M1, L1, L2 and N is 0 or a positive number, satisfying0≦M1/(M1+L1+L2+N+M2)≦0.8, 0≦L1/(M1+L1+L2+N+M2)≦0.8,0≦L2/(M1+L1+L2+N+M2)≦0.8, 0≦N/(M1+L1+L2+N+M2)≦0.8, and M1+L1+L2+N+M2=1.L1, L2 and N are not equal to 0 at the same time. Each of u and w is 0or a positive integer, and v is a positive integer, satisfying u+v+w≦5.Letters x and y are as defined above.

More preferably, M1, L1, L2, N and M2 satisfy the following ranges.

0≦M1/(M1+L1+L2+N+M2)≦0.5,

especially 0.002≦M1/(M1+L1+L2+N+M2)≦0.2

0≦L1/(M1+L1+L2+N+M2)≦0.5,

especially 0≦L1/(M1+L1+L2+N+M2)≦0.4

0≦L2/(M1+L1+L2+N+M2)≦0.5,

especially 0≦L2/(M1+L1+L2+N+M2)≦0.4

0≦N/(M1+L1+L2+N+M2)≦0.5,

especially 0≦N/(M1+L1+L2+N+M2)≦0.4

0.4≦M2/(M1+L1+L2+N+M2)≦1,

especially 0.5≦M2/(M1+L1+L2+N+M2)≦0.9

0≦(L1+L2+N/)/(M1+L1+L2+N+M2)≦0.5,

especially 0.1≦(L1+L2+N/)/(M1+L1+L2+N+M2)≦0.4

It is also preferred that N/(L1+L2+N) be from 0 to 1, more preferablyfrom 0.5 to 1, and most preferably from 0.7 to 1.

In this polymer as well, the total amount of the acid labile groups andcrosslinking groups is, on the average, more than 0 mol % to 80 mol %based on the entire phenolic hydroxyl groups in formula (2b) or thephenolic hydroxyl groups and carboxyl groups in formula (2b′) combined.

Examples of this polymer are those comprising recurring units of thefollowing formulae (2b′-1) to (2b′-7).

In the above formulae, h″ is equal to 0 or 1, y is an integer of 1 to 3,U1, U2 and U3 stand for the following units, respectively.

It is noted that u+w=x. Q is a crosslinking group having a C—O—Clinkage, typically a crosslinking group represented by the above formula(3a) or (3b), especially a crosslinking group represented by the aboveformula (3a″), (3b″) or (3a″′), (3b″′), and preferably (3a′) or (3b′).It is noted that where the crosslinking group Q is trivalent orpolyvalent, Q is attached to at least three units of the followingformula in formula (2b).

It is noted that the above formulae (2b′-2) and (2b′-5) showintramolecular bonded states and the remaining formulae showintermolecular bonded states, which may be present alone or inadmixture.

Where the resin in the resist composition according to the invention iscrosslinked with acid labile substituents, it is a polymer which isobtained by reacting phenolic hydroxyl groups with an alkenyl ethercompound or halogenated alkyl ether such that the polymer is crosslinkedwithin a molecular and/or between molecules with crosslinking groupshaving C—O—C linkages, wherein the total amount of the acid labilegroups and crosslinking groups is preferably, on the average, more than0 mol % to 80 mol %, especially 2 to 50 mol %, based on the entirephenolic hydroxyl groups in formula (2) or the phenolic hydroxyl groupsand carboxyl groups in formula (2′) combined.

An appropriate proportion of crosslinking groups having C—O—C linkagesis, on the average, from more than 0 mol % to 50 mol %, and especiallyfrom 0.2 to 20 mol %. With 0 mol %, few benefits of the crosslinkinggroup are obtained, resulting in a reduced contrast of alkalidissolution rate and a low resolution. With more than 50 mol %, a toomuch crosslinked polymer would gel, become insoluble in alkali, induce afilm thickness change, internal stresses or bubbles upon alkalidevelopment, and lose adhesion to the substrate due to less hydrophilicgroups.

The proportion of acid labile groups is on the average preferably frommore than 0 mol % to 80 mol %, especially from 10 to 50 mol %. With 0mol %, there may result a reduced contrast of alkali dissolution rateand low resolution. With more than 80 mol %, there may result a loss ofalkali dissolution, less affinity to an alkali developer upondevelopment, and a low resolution.

By properly selecting the proportions of crosslinking groups havingC—O—C linkages and acid labile groups within the above-defined ranges,it becomes possible to control the size and configuration of a resistpattern as desired. In the resist composition comprising the onium saltaccording to the invention, the contents of crosslinking groups havingC—O—C linkages and acid labile groups in the polymer have substantialinfluence on the dissolution rate contrast of a resist film and governthe properties of the resist composition relating to the size andconfiguration of a resist pattern.

Now A in the crosslinking group is described. The (a′+1)-valent organicgroups represented by A include hydrocarbon groups, for example,substituted or unsubstituted alkylene groups preferably having 1 to 50carbon atoms, and especially 1 to 40 carbon atoms, substituted orunsubstituted arylene groups preferably having 6 to 50 carbon atoms, andespecially 6 to 40 carbon atoms (these alkylene and arylene groups mayhave an intervening hetero atom or group such as O, NH, N(CH₃), S orSO₂, and where substituted, the substituents are hydroxyl, carboxyl,acyl and fluorine), and combinations of these alkylene groups with thesearylene groups. Additional examples include (a′+1)-valent heterocyclicgroups, and combinations of these heterocyclic groups with the foregoinghydrocarbon groups.

Illustrative examples of A are given below.

 —CH₂—CH₂—, —(CH₂)₃—,

 —(CH₂)₄—

 —(CH₂)₅—,

 —(CH₂)₆—,

 —(CH₂CH₂O)₃—CH₂CH₂,

 (CH₂)₄—O—(CH₂)₄_(5˜10),

—CH₂—CH₂—O—CH₂—CH₂—, —CH₂—CH₂—O—CH₂—CH₂—O—CH₂CH₂—,

Preferably, in formula (3a), R⁷ is methyl, R⁸ is hydrogen, b is equal to0, and A is ethylene, 1,4-butylene or 1,4-cyclohexylene.

In preparing the polymer which is crosslinked within a molecular and/orbetween molecules with crosslinking groups having C—O—C linkages,synthesis may be made by reacting a corresponding non-crosslinkedpolymer with an alkenyl ether in the presence of an acid catalyst in aconventional manner.

Alternatively, where decomposition of other acid labile groups takesplace in the presence of an acid catalyst, the end product can besynthesized by first reacting an alkenyl ether with hydrochloric acid orthe like to form a halogenated alkyl ether, and reacting it with apolymer under basic conditions in a conventional manner.

Illustrative, non-limiting, examples of the alkenyl ether includeethylene glycol divinyl ether, triethylene glycol divinyl ether,1,2-propanediol divinyl ether, 1,3-propanediol divinyl ether,1,3-butanediol divinyl ether, 1,4-butanediol divinyl ether,tetramethylene glycol divinyl ether, neopentyl glycol divinyl ether,trimethylolpropane trivinyl ether, trimethylolethane trivinyl ether,hexanediol divinyl ether, 1,4-cyclohexanediol divinyl ether,1,4-divinyloxymethylcyclohexane, tetraethylene glycol divinyl ether,pentaerythritol divinyl ether, pentaerythritol trivinyl ether,pentaerythritol tetravinyl ether, sorbitol tetravinyl ether, sorbitolpentavinyl ether, ethylene glycol diethylene vinyl ether, triethyleneglycol diethylene vinyl ether, ethylene glycol dipropylene vinyl ether,triethylene glycol diethylene vinyl ether, trimethylolpropanetriethylene vinyl ether, trimethylolpropane diethylene vinyl ether,pentaerythritol diethylene vinyl ether, pantaerythritol triethylenevinyl ether, pentaerythritol tetraethylene vinyl ether, and thecompounds of the following formulae (I-1) through (I-31).

Also useful are terephthalic acid diethylene vinyl ether, phthalicn aciddiethylene vinyl ether, isophthalic acid diethylene vinyl ether,phthalic acid dipropylene vinyl ether, terephthalic acid dipropylenevinyl ether isophthalic acid dipropylene vinyl ether, maleic aciddiethylene vinyl ether, fumaric acid diethylene vinyl ether, itaconicacid diethylene vinyl ether as well as the compounds of the followingformulae (II-1) through (II11). Useful alkenyl ethers are not limited tothese examples.

In the resist composition according to the invention, the resin used ascomponent (A) is as described above while the preferred acid labilegroups introduced therein are 1-ethylcyclohexyl, 1-ethylcyclopentyl,1-ethylcyclohexyloxycarbonylmethyl, tert-amyl, 1-ethoxyethyl,1-ethoxypropyl, tetrahydrofuranyl, tetrahydropyranyl, tert-butyl,tert-butoxycarbonyl, tert-butoxycarbonylmethyl groups, and substituentsof formula (3a) wherein R⁷ is methyl, R⁸ is hydrogen, a′ is equal to 1,b is equal to 0, and A is ethylene, 1,4-butylene or 1,4-cyclohexylene.

In a single polymer, these substituents may be incorporated alone or inadmixture of two or more types. A blend of two or more polymers havingsubstituents of different types is also acceptable.

Appropriate combinations of substituents of two or more types include acombination of acetal with acetal analog, a combination of acetal with asubstituent having a different degree of scission by acid such astert-butoxy, a combination of a crosslinking acid labile group withacetal, and a combination of a crosslinking acid labile group with asubstituent having a different degree of cleavage by acid such astert-butoxy.

The percent proportion of these substituents substituting for phenol andcarboxyl groups in the polymer is not critical. Preferably thesubstitution rate is selected such that when a resist compositioncomprising the polymer is applied onto a substrate to form a coating,the unexposed area of the coating may have a dissolution rate of 0.01 to10 Å/sec in a 2.38% tetramethylammonium hydroxide (TMAH) developer.

On use of a polymer containing a greater proportion of carboxyl groupswhich can increase the alkali dissolution rate, the substitution ratemust be increased or non-acid-labile substituents to be described latermust be introduced.

When acid labile groups for intramolecular and/or intermolecularcrosslinking are to be introduced, the percent proportion ofcrosslinking substituents is preferably up to 20%, more preferably up to10%. If the substitution rate of crosslinking substituents is too high,crosslinking results in a higher molecular weight which can adverselyaffect dissolution, stability and resolution. It is also preferred tofurther introduce another non-crosslinking acid labile group into thecrosslinked polymer at a substitution rate of up to 10% for adjustingthe dissolution rate to fall within the above range.

In the case of poly(p-hydroxystyrene), the optimum substitution ratediffers between a substituent having a strong dissolution inhabitationsuch as a tert-butoxycarbonyl group and substituent having a weakdissolution inhabitation such as an acetal group although the overallsubstitution rate is preferably 10 to 40%, more preferably 20 to 30%.

Polymers having such acid labile groups introduced therein shouldpreferably have a weight average molecular weight (Mw) of 3,000 to100,000. With a Mw of less than 3,000, polymers would perform poorly andoften lack heat resistance and film formability. Polymers with a Mw ofmore than 100,000 would be less soluble in a developer and a resistsolvent.

Where non-crosslinking acid labile groups are introduced, the polymershould preferably have a dispersity (Mw/Mn) of up to 3.5, preferably upto 1.5. A polymer with a dispersity of more than 3.5 often results in alow resolution. Where crosslinking acid labile groups are introduced,the starting alkali-soluble resin should preferably have a dispersity(Mw/Mn) of up to 1.5, and the dispersity is kept at 3 or lower evenafter protection with crosslinking acid labile groups. If the dispersityis higher than 3, dissolution, coating, storage stability and/orresolution is often poor.

To impart a certain function, suitable substituent groups may beintroduced into some of the phenolic hydroxyl and carboxyl groups on theacid labile group-protected polymer. Exemplary are substituent groupsfor improving adhesion to the substrate, non-acid-labile groups foradjusting dissolution in an alkali developer, and substituent groups forimproving etching resistance. Illustrative, non-limiting, substituentgroups include 2-hydroxyethyl, 2-hydroxypropyl, methoxymethyl,methoxycarbonyl, ethoxycarbonyl, methoxycarbonylmethyl,ethoxycarbonylmethyl, 4-methyl-2-oxo-4-oxoranyl,4-methyl-2-oxo-4-oxanyl, methyl, ethyl, propyl, n-butyl, sec-butyl,acetyl, pivaloyl, adamantyl, isobornyl, and cyclohexyl.

Illustrative examples of the onium salts of formulae (1), (1a), (1a′)and (1b) as the photoacid generator are as described above, but listedagain.

The onium salts according to the invention are salts ofsulfonyloxybenzenesulfonate anions with iodonium or sulfonium cations.Exemplary anions include a4-(4′-methylphenylsulfonyloxy)benzenesulfonate anion,4-(4′-methoxyphenylsulfonyloxy)benzenesulfonate anion,4-phenylsulfonyloxybenzenesulfonate anion,4-(2′,4′,6′-trimethylphenylsulfonyloxy)benzenesulfonate anion,4-(2′-naphthylsulfonyloxy)benzenesulfonate anion,4-(10′-camphorsulfonyloxy)benzenesulfonate anion,4-methanesulfonyloxybenzenesulfonate anion,4-(n-butanesulfonyloxy)benzenesulfonate anion,2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate anion, and2,5-bis(phenylsulfonyloxy)benzenesulfonate anion. Of these, preferredanions are 4-(4′-methylphenylsulfonyloxy)benzenesulfonate,4-(4′-methoxyphenylsulfonyloxy)benzenesulfonate,4-(10′-camphorsulfonyloxy)benzenesulfonate,2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate, and2,5-bis(phenylsulfonyloxy)benzenesulfonate anions, and(4′-methylphenylsulfonyloxy)-methylbenzenesulfonate anions in which theposition of the substituents is not limited.

Exemplary iodonium cations include diphenyliodonium,bis(4-tert-butylphenyl)iodonium, 4-methoxyphenylphenyliodonium,4-ethoxyphenyl-phenyliodonium, and 4-tert-butoxyphenyl-phenyliodonium,with the diphenyliodonium and bis(4-tert-butylphenyl)iodonium arepreferred.

Exemplary sulfonium cations include triphenylsulfonium,4-hydroxyphenyldiphenylsulfonium, (4-tert-butylphenyl)diphenylsulfonium,bis(4-tert-butylphenyl)-phenylsulfonium,tris(4-tert-butylphenyl)sulfonium, 4-methylphenyldiphenylsulfonium,bis(4-methylphenyl)phenylsulfonium, tris(4-methylphenyl)sulfonium,(4-tert-butoxyphenyl)diphenylsulfonium,bis(4-tert-butoxyphenyl)-phenylsulfonium,tris(4-tert-butoxyphenyl)sulfonium,(3-tert-butoxyphenyl)diphenylsulfonium,bis(3-tert-butoxyphenyl)phenylsulfonium,tris(3-tert-butoxyphenyl)-sulfonium,(3,4-di-tert-butoxyphenyl)diphenylsulfonium,bis(3,4-di-tert-butoxyphenyl)phenylsulfonium,tris(3,4-di-tert-butoxyphenyl)sulfonium,diphenyl(4-thiophenoxyphenyl)sulfonium,(4-tert-butoxycarbonylmethyloxyphenyl)diphenylsulfonium,tris(4-tert-butoxycarbonylmethyloxyphenyl)sulfonium,(4-tert-butoxyphenyl)bis(4-dimethylaminophenyl)sulfonium,tris(4-methoxyphenyl)sulfonium, tris(4-ethoxyphenyl)sulfonium,tris(4-dimethylaminophenyl)sulfonium, 2-naphthyldiphenylsulfonium,dimethyl-2-naphthylsulfonium, 4-hydroxyphenyldimethylsulfonium,4-methoxyphenyldimethylsulfonium, dimethylphenylsulfonium,diphenylmethylsulfonium, trimethylsulfonium,2-oxocyclohexylcyclohexylmethylsulfonium,2-oxocyclohexyl-methylhenylsulfonium,2-oxocyclopentyl-methyl-phenylsulfonium,2-oxopropyl-methyl-phenylsulfonium, and tribenzylsulfonium. Of these,preferred are triphenylsulfonium, 4-tert-butoxyphenyldiphenylsulfonium,diphenylmethylsulfonium, dimethylphenylsulfonium,4-tert-butylphenyldiphenylsulfonium, tris(4-methylphenyl)sulfonium, andtris(4-tert-butylphenyl)sulfonium.

Especially useful onium salts are: triphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate,4-tert-butoxyphenyldiphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate,4-tert-butylphenyldiphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate, dimethylphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate,tris(4-tert-butoxyphenyl)sulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate,tris(4-methylphenyl)sulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate,tris(4-tert-butylphenyl)sulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate, triphenylsulfonium4-(10′-camphorsulfonyloxy)benzenesulfonate,4-tert-butoxyphenyldiphenylsulfonium4-(10′-camphorsulfonyloxy)benzenesulfonate,4-tert-butylphenyldiphenylsulfonium4-(10′-camphorsulfonyloxy)benzenesulfonate, dimethylphenylsulfonium4-(10′-camphorsulfonyloxy)benzenesulfonate,tris(4-tert-butoxyphenyl)sulfonium4-(10′-camphorsulfonyloxy)benzenesulfonate, diphenyliodonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate,bis(4-tert-butylphenyl)iodonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate,bis(4-tert-butylphenyl)iodonium4-(10′-camphorsulfonyloxy)benzenesulfonate, triphenylsulfonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate,tris(4-methylphenyl)sulfonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate,tris(4-tert-butylphenyl)sulfonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate, andbis(4-tert-butylphenyl)iodonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate.

In the chemical amplification type resist composition, an appropriateamount of the onium salt (B) of formula (1), (1a), (1a′) or (1b) addedis from 0.5 part to 20 parts by weight, and preferably from 1 to 10parts by weight, per 100 parts by weight of the solids in thecomposition. The photoacid generators may be used alone or in admixtureof two or more. The transmittance of the resist film can be controlledby using a photoacid generator having a low transmittance at theexposure wavelength and adjusting the amount of the photoacid generatoradded.

Component (C)

In one preferred embodiment, the resist composition further contains (C)a compound capable of generating an acid upon exposure to high energyradiation, that is, a second photoacid generator other than the oniumsalt (B). Examples of the second photoacid generator are given belowwhile they may be used alone or in admixture of two or more.

Sulfonium salts are salts of sulfonium cations with sulfonates (sulfonicacid anions). Exemplary sulfonium cations include triphenylsulfonium,(4-tert-butoxyphenyl)diphenylsulfonium,bis(4-tert-butoxyphenyl)phenylsulfonium,4-methylphenyldiphenylsulfonium, tris(4-methylphenyl)sulfonium,4-tert-butylphenyldiphenylsulfonium, tris(4-tert-butylphenyl)sulfonium,tris(4-tert-butoxyphenyl)sulfonium,(3-tert-butoxyphenyl)diphenylsulfonium,bis(3-tert-butoxyphenyl)phenylsulfonium,tris(3-tert-butoxyphenyl)sulfonium,(3,4-di-tert-butoxyphenyl)diphenylsulfonium,bis(3,4-di-tert-butoxyphenyl)phenylsulfonium,tris(3,4-di-tert-butoxyphenyl)sulfonium,diphenyl(4-thiophenoxyphenyl)sulfonium,(4-tert-butoxycarbonylmethyloxyphenyl)diphenylsulfonium,tris(4-tert-butoxycarbonylmethyloxyphenyl)sulfonium,(4-tert-butoxyphenyl)bis(4-dimethylaminophenyl)sulfonium,tris(4-dimethylaminophenyl)sulfonium, 2-naphthyldiphenylsulfonium,dimethyl-2-naphthylsulfonium, 4-hydroxyphenyldimethylsulfonium,4-methoxyphenyldimethylsulfonium, trimethylsulfonium,diphenylmethylsulfonium, methyl-2-oxopropylphenylsulfonium,2-oxocyclohexylcyclohexylmethylsulfonium, trinaphthylsulfonium, andtribenzylsulfonium. Exemplary sulfonates includetrifluoromethanesulfonate, nonafluorobutanesulfonate,heptadecafluorooctanesulfonate, 2,2,2-trifluoroethanesulfonate,pentafluorobenzenesulfonate, 4-trifluoromethylbenzenesulfonate,4-fluorobenzenesulfonate, toluenesulfonate, benzenesulfonate,naphthalenesulfonate, camphorsulfonate, octanesulfonate,dodecylbenzenesulfonate, butanesulfonate, and methanesulfonate.Sulfonium salts based on combination of the foregoing examples areincluded.

Iodinium salts are salts of iodonium cations with sulfonates (sulfonicacid anions). Exemplary iodinium cations are aryliodonium cationsincluding diphenyliodinium, bis(4-tert-butylphenyl)iodonium,4-tert-butoxyphenylphenyliodonium, and 4-methoxyphenylphenyliodonium.Exemplary sulfonates include trifluoromethanesulfonate,nonafluorobutanesulfonate, heptadecafluorooctanesulfonate,2,2,2-trifluoroethanesulfonate, pentafluorobenzenesulfonate,4-trifluoromethylbenzenesulfonate, 4-fluorobenzenesulfonate,toluenesulfonate, benzenesulfonate, naphthalenesulfonate,camphorsulfonate, octanesulfonate, dodecylbenzenesulfonate,butanesulfonate, and methanesulfonate. Iodonium salts based oncombination of the foregoing examples are included.

Exemplary sulfonyldiazomethane compounds include bissulfonyldiazomethanecompounds and sulfonyl-carbonyldiazomethane compounds such asbis(ethylsulfonyl)diazomethane, bis(1-methylpropylsulfonyl)diazomethane,bis(2-methylpropylsulfonyl)diazomethane,bis(1,1-dimethylethylsulfonyl)diazomethane,bis(cyclohexylsulfonyl)diazomethane,bis(perfluoroisopropylsulfonyl)diazomethane,bis(phenylsulfonyl)diazomethane,bis(4-methylphenylsulfonyl)diazomethane,bis(2,4-dimethylphenylsulfonyl)diazomethane,bis(2-naphthylsulfonyl)diazomethane,4-methylphenylsulfonylbenzoyldiazomethane,tert-butylcarbonyl-4-methylphenylsulfonyldiazomethane,2-naphthylsulfonylbenzoyldiazomethane,4-methylphenylsulfonyl-2-naphthoyldiazomethane,methylsulfonylbenzoyldiazomethane, andtert-butoxycarbonyl-4-methylphenylsulfonyldiazomethane.

N-sulfonyloxyimide photoacid generators include combinations of imideskeletons with sulfonates. Exemplary imide skeletons are succinimide,naphthalene dicarboxylic acid imide, phthalimide, cyclohexyldicarboxylicacid imide, 5-norbornene-2,3-dicarboxylic acid imide, and7-oxabicyclo[2.2.1]-5-heptene-2,3-dicarboxylic acid imide. Exemplarysulfonates include trifluoromethanesulfonate, nonafluorobutanesulfonate,heptadecafluorooctanesulfonate, 2,2,2-trifluoroethanesulfonate,pentafluorobenzenesulfonate, 4,-trifluoromethylbenzenesulfonate,4-fluorobenzenesulfonate, toluenesulfonate, benzenesulfonate,naphthalenesulfonate, camphorsulfonate, octanesulfonate,dodecylbenzenesulfonate, butanesulfonate, and methanesulfonate.

Benzoinsulfonate photoacid generators include benzoin tosylate, benzoinmesylate, and benzoin butanesulfonate.

Pyrogallol trisulfonate photoacid generators include pyrogallol,fluoroglycine, catechol, resorcinol, hydroquinone, in which all thehydroxyl groups are replaced by trifluoromethanesulfonate,nonafluorobutanesulfonate, heptadecafluorooctanesulfonate,2,2,2-trifluoroethanesulfonate, pentafluorobenzenesulfonate,4-trifluoromethylbenzenesulfonate, 4-fluorobenzenesulfonate,toluenesulfonate, benzenesulfonate, naphthalenesulfonate,camphorsulfonate, octanesulfonate, dodecylbenzenesulfonate,butanesulfonate, and methanesulfonate.

Nitrobenzyl sulfonate photoacid generators include 2,4-dinitrobenzylsulfonate, 2-nitrobenzyl sulfonate, and 2,6-dinitrobenzyl sulfonate,with exemplary sulfonates including trifluoromethanesulfonate,nonafluorobutanesulfonate, heptadecafluorooctanesulfonate,2,2,2-trifluoroethanesulfonate, pentafluorobenzenesulfonate,4-trifluoromethylbenzenesulfonate, 4-fluorobenzenesulfonate,toluenesulfonate, benzenesulfonate, naphthalenesulfonate,camphorsulfonate, octanesulfonate, dodecylbenzenesulfonate,butanesulfonate, and methanesulfonate. Also useful are analogousnitrobenzyl sulfonate compounds in which the nitro group on the benzylside is replaced by a trifluoromethyl group.

Sulfone photoacid generators include bis(phenylsulfonyl)methane,bis(4-methylphenylsulfonyl)methane, bis(2-naphthylsulfonyl)methane,2,2-bis(phenylsulfonyl)propane, 2,2-bis(4-methylphenylsulfonyl)propane,2,2-bis(2-naphthylsulfonyl)propane,2-methyl-2-(p-toluenesulfonyl)propiophenone,2-cyclohexylcarbonyl-2-(p-toluenesulfonyl)propane, and2,4-dimethyl-2-(p-toluenesulfonyl)pentan-3-one.

Photoacid generators in the form of glyoxime derivatives includebis-o-(p-toluenesulfonyl)-α-dimethylglyoxime,bis-o-(p-toluenesulfonyl)-α-diphenylglyoxime,bis-o-(p-toluenesulfonyl)-α-dicyclohexylglyoxime,bis-o-(p-toluenesulfonyl)-2,3-pentanedioneglyoxime,bis-o-(p-toluenesulfonyl)-2-methyl-3,4-pentanedioneglyoxime,bis-o-(n-butanesulfonyl)-α-dimethylglyoxime,bis-o-(n-butanesulfonyl)-α-diphenylglyoxime,bis-o-(n-butanesulfonyl)-α-dicyclohexylglyoxime,bis-o-(n-butanesulfonyl)-2,3-pentanedioneglyoxime,bis-o-(n-butanesulfonyl)-2-methyl-3,4-pentanedioneglyoxime,bis-o-(methanesulfonyl)-a-dimethylglyoxime,bis-o-(trifluoromethanesulfonyl)-α-dimethylglyoxime,bis-o-(1,1,1-trifluoroethanesulfonyl)-α-dimethylglyoxime,bis-o-(tert-butanesulfonyl)-α-dimethylglyoxime,bis-o-(perfluorooctanesulfonyl)-α-dimethylglyoxime,bis-o-(cyclohexylsulfonyl)-α-dimethylglyoxime,bis-o-(benzenesulfonyl)-α-dimethylglyoxime,bis-o-(p-fluorobenzenesulfonyl)-α-dimethylglyoxime,bis-o-(p-tert-butylbenzenesulfonyl)-α-dimethylglyoxime,bis-o-(xylenesulfonyl)-α-dimethylglyoxime, andbis-o-(camphorsulfonyl)-α-dimethylglyoxime.

Of these photoacid generators, the sulfonium salts,bissulfonyldiazomethane compounds, and N-sulfonyloxyimide compounds arepreferred. While the anion of the optimum acid to be generated differsdepending on the ease of scission of acid labile groups introduced inthe polymer, an anion which is non-volatile and not extremely diffusiveis generally chosen. The preferred anions include benzenesulfonic acidanions, toluenesulfonic acid anions, pentafluorobenzenesulfonic acidanions, 2,2,2-trifluoroethanesulfonic acid anions,nonafluorobutanesulfonic acid anions, heptadecafluorooctanesulfonic acidanions, and camphorsulfonic acid anions.

In the resist composition comprising the onium salt as the firstphotoacid generator according to the invention, an appropriate amount ofthe second photoacid generator is 0 to 20 parts, and especially 1 to 10parts by weight per 100 parts by weight of the solids in thecomposition. The second photoacid generators may be used alone or inadmixture of two or more. The transmittance of the resist film can becontrolled by using a (second) photoacid generator having a lowtransmittance at the exposure wavelength and adjusting the amount of thephotoacid generator added.

In the resist composition according to the invention, there may be added(D) a compound which is decomposed with an acid to generate an acid,that is, acid-propagating compound. For these compounds, referenceshould be made to J. Photopolym. Sci. and Tech., 8, 43-44, 45-46 (1995),and ibid., 9, 29-30 (1996).

Examples of the acid-propagating compound include 5tert-butyl-2-methyl-2-tosyloxymethyl acetoacetate and2-phenyl-2-(tosyloxyethyl)-1,3-dioxoran, but are not limited thereto. Ofwell-known photoacid generators, many of those compounds having poorstability, especially poor thermal stability exhibit an acid-propagatingcompound-like behavior.

In the resist composition according to the invention, an appropriateamount of the acid-propagating compound is up to 2 parts, and especiallyup to 1 part by weight per 100 parts by weight of the solids in thecomposition. Excessive amounts of the acid-propagating compound makesdiffusion control difficult, leading to degradation of resolution andpattern configuration.

Component (F)

In one preferred embodiment, the resist composition further contains (F)a compound with a molecular weight of up to 3,000 which changes itssolubility in an alkaline developer under the action of an acid, thatis, a dissolution inhibitor. Typically, a compound obtained by partiallyor entirely substituting acid labile substituents on a phenol orcarboxylic acid derivative having a molecular weight of up to 2,500 isadded as the dissolution inhibitor.

Examples of the phenol or carboxylic acid derivative having a molecularweight of up to 2,500 include bisphenol A, bisphenol H, bisphenol S,4,4-bis(4′-hydroxyphenyl)valeric acid, tris(4-hydroxyphenyl)methane,1,1,1-tris(4′-hydroxyphenyl)ethane, 1,1,2-tris(4′-hydroxyphenyl)ethane,phenolphthalein, and thimolphthalein. The acid labile substituents arethe same as those exemplified as the acid labile groups in the polymer.

Illustrative, non-limiting, examples of the dissolution inhibitors whichare useful herein include bis(4-(2′-tetrahydropyranyloxy)phenyl)methane,bis(4-(2′-tetrahydrofuranyloxy)phenyl)methane, bis(4-tert-butoxyphenyl)methane, bis(4-tert-butoxycarbonyloxyphenyl)methane,bis(4-tert-butoxycarbonylmethyloxyphenyl)methane,bis(4-(1′-ethoxyethoxy)phenyl)methane,bis(4-(4′-ethoxypropyloxy)phenyl)methane,2,2-bis(4′-(2″-tetrahydropyranyloxy))propane,2,2-bis(4′-(2″-tetrahydrofuranyloxy)phenyl)propane,2,2-bis(4′-tert-butoxyphenyl)propane,2,2-bis(4′-tert-butoxycarbonyloxyphenyl)propane,2,2-bis(4-tert-butoxycarbonylmethyloxyphenyl)propane,2,2-bis(4′-(1″-ethoxyethoxy)phenyl)propane,2,2-bis(4′-(1″-ethoxypropyloxy)phenyl)propane, tert-butyl4,4-bis(4′-(2″-tetrahydropyranyloxy)phenyl)valerate, tert-butyl4,4-bis(4′-(2″-tetrahydrofuranyloxy)phenyl)valerate, tert-butyl4,4-bis(4′-tert-butoxyphenyl)valerate, tert-butyl4,4-bis(4-tert-butoxycarbonyloxyphenyl)valerate, tert-butyl4,4-bis(4′-tert-butoxycarbonylmethyloxyphenyl)valerate, tert-butyl4,4-bis(4′-(1″-ethoxyethoxy)phenyl)valerate, tert-butyl4,4-bis(4′-(1″-ethoxypropyloxy)phenyl)valerate,tris(4-(2′-tetrahydropyranyloxy)phenyl)methane,tris(4-(2′-tetrahydrofuranyloxy)phenyl)methane,tris(4-tert-butoxyphenyl)methane,tris(4-tert-butoxycarbonyloxyphenyl)methane,tris(4-tert-butoxycarbonyloxymethylphenyl)methane,tris(4-(1′-ethoxyethoxy)phenyl)methane,tris(4-(1′-ethoxypropyloxy)phenyl)methane,1,1,2-tris(4′-(2″-tetrahydropyranyloxy)phenyl)ethane,1,1,2-tris(4′-(2″-tetrahydrofuranyloxy)phenyl)ethane,1,1,2-tris(4′-tert-butoxyphenyl)ethane,1,1,2-tris(4′-tert-butoxycarbonyloxyphenyl)ethane,1,1,2-tris(4′-tert-butoxycarbonylmethyloxyphenyl)ethane,1,1,2-tris(4′-(1′-ethoxyethoxy)phenyl)ethane, and1,1,2-tris(4′-(1′-ethoxypropyloxy)phenyl)ethane.

In the resist composition according to the invention, an appropriateamount of the dissolution inhibitor (F) is up to 20 parts, andespecially up to 15 parts by weight per 100 parts by weight of thesolids in the composition. With more than 20 parts of the dissolutioninhibitor, the resist composition becomes less heat resistant because ofan increased content of monomer components.

Component (G)

The basic compound used as component (G) is preferably a compoundcapable of suppressing the diffusion length when the acid generated bythe photoacid generator diffuses within the resist film. The inclusionof this type of basic compound holds down the acid diffusion lengthwithin the resist film, resulting in better resolution. In addition, itsuppresses changes in sensitivity following exposure and reducessubstrate and environment dependence, as well as improving the exposurelatitude and the pattern profile.

Examples of basic compounds include primary, secondary, and tertiaryaliphatic amines, mixed amines, aromatic amines, heterocyclic amines,carboxyl group-bearing nitrogenous compounds, sulfonyl group-bearingnitrogenous compounds, hydroxyl group-bearing nitrogenous compounds,hydroxyphenyl group-bearing nitrogenous compounds, alcoholic nitrogenouscompounds, amide derivatives, and imide derivatives.

Examples of suitable primary aliphatic amines include ammonia,methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine,isobutylamine, sec-butylamine, tert-butylamine, pentylamine,tert-amylamine, cyclopentylamine, hexylamine, cyclohexylamine,heptylamine, octylamine, nonylamine, decylamine, dodecylamine,cetylamine, methylenediamine, ethylenediamine, andtetraethylenepentamine. Examples of suitable secondary aliphatic aminesinclude dimethylamine, diethylamine, di-n-propylamine, diisopropylamine,di-n-butylamine, diisobutylamine, di-sec-butylamine, dipentylamine,dicyclopentylamine, dihexylamine, dicyclohexylamine, diheptylamine,dioctylamine, dinonylamine, didecylamine, didodecylamine, dicetylamine,N,N-dimethylmethylenediamine, N,N-dimethylethylenediamine, andN,N-dimethyltetraethylenepentamine. Examples of suitable tertiaryaliphatic amines include trimethylamine, triethylamine,tri-n-propylamine, triisopropylamine, tri-n-butylamine,triisobutylamine, tri-sec-butylamine, tripentylamine,tricyclopentylamine, trihexylamine, tricyclohexylamine, triheptylamine,trioctylamine, trinonylamine, tridecylamine, tridodecylamine,tricetylamine, N,N,N′,N′-tetramethylmethylenediamine,N,N,N′,N′-tetramethylethylenediamine, andN,N,N′,N′-tetramethyltetraethylenepentamine.

Examples of suitable mixed amines include dimethylethylamine,methylethylpropylamine, benzylamine, phenethylamine, andbenzyldimethylamine. Examples of suitable aromatic and heterocyclicamines include aniline derivatives (e.g., aniline, N-methylaniline,N-ethylaniline, N-propylaniline, N,N-dimethylaniline, 2-methylaniline,3-methylaniline, 4-methylaniline, ethylaniline, propylaniline,trimethylaniline, 2-nitroaniline, 3-nitroaniline, 4-nitroaniline,2,4-dinitroaniline, 2,6-dinitroaniline, 3,5-dinitroaniline, andN,N-dimethyltoluidine), diphenyl(p-tolyl)amine, methyldiphenylamine,triphenylamine, phenylenediamine, naphthylamine, diaminonaphthalene,pyrrole derivatives (e.g., pyrrole, 2H-pyrrole, 1-methylpyrrole,2,4-dimethylpyrrole, 2,5-dimethylpyrrole, and N-methylpyrrole), oxazolederivatives (e.g., oxazole and isooxazole), thiazole derivatives (e.g.,thiazole and isothiazole), imidazole derivatives (e.g., imidazole,4-methylimidazole, and 4-methyl-2-phenylimidazole), pyrazolederivatives, furazan derivatives, pyrroline derivatives (e.g., pyrrolineand 2-methyl-1-pyrroline), pyrrolidine derivatives (e.g., pyrrolidine,N-methylpyrrolidine, pyrrolidinone, and N-methylpyrrolidone),imidazoline derivatives, imidazolidine derivatives, pyridine derivatives(e.g., pyridine, methylpyridine, ethylpyridine, propylpyridine,butylpyridine, 4-(1-butylpentyl)pyridine, dimethylpyridine,trimethylpyridine, triethylpyridine, phenylpyridine,3-methyl-2-phenylpyridine, 4-tert-butylpyridine, diphenylpyridine,benzylpyridine, methoxypyridine, butoxypyridine, dimethoxypyridine,1-methyl-2-pyridine, 4-pyrrolidinopyridine, 1-methyl-4-phenylpyridine,2-(1-ethylpropyl)pyridine, aminopyridine, and dimethylaminopyridine),pyridazine derivatives, pyrimidine derivatives, pyrazine derivatives,pyrazoline derivatives, pyrazolidine derivatives, piperidinederivatives, piperazine derivatives, morpholine derivatives, indolederivatives, isoindole derivatives, 1H-indazole derivatives, indolinederivatives, quinoline derivatives (e.g., quinoline and3-quinolinecarbonitrile), isoquinoline derivatives, cinnolinederivatives, quinazoline derivatives, quinoxaline derivatives,phthalazine derivatives, purine derivatives, pteridine derivatives,carbazole derivatives, phenanthridine derivatives, acridine derivatives,phenazine derivatives, 1,10-phenanthroline derivatives, adeninederivatives, adenosine derivatives, guanine derivatives, guanosinederivatives, uracil derivatives, and uridine derivatives.

Examples of suitable carboxyl group-bearing nitrogenous compoundsinclude aminobenzoic acid, indolecarboxylic acid, and amino acidderivatives (e.g. nicotinic acid, alanine, alginine, aspartic acid,glutamic acid, glycine, histidine, isoleucine, glycylleucine, leucine,methionine, phenylalanine, threonine, lysine,3-aminopyrazine-2-carboxylic acid, and methoxyalanine). Examples ofsuitable sulfonyl group-bearing nitrogenous compounds include3-pyridinesulfonic acid and pyridinium p-toluenesulfonate. Examples ofsuitable hydroxyl group-bearing nitrogenous compounds, hydroxyphenylgroup-bearing nitrogenous compounds, and alcoholic nitrogenous compoundsinclude 2-hydroxypyridine, aminocresol, 2,4-quinolinediol,3-indolemethanol hydrate, monoethanolamine, diethanolamine,triethanolamine, N-ethyldiethanolamine, N,N-diethylethanolamine,truisopropanolamine, 2,2′-iminodiethanol, 2-aminoethanol,3-amino-1-propanol, 4-amino-1-butanol, 4-(2-hydroxyethyl)morpholine,2-(2-hydroxyethyl)pyridine, 1-(2-hydroxyethyl)piperazine,1-[2-(2-hydroxyethoxy)ethyl]-piperazine, piperidine ethanol,1-(2-hydroxyethyl)pyrrolidine, 1-(2-hydroxyethyl)-2-pyrrolidinone,3-piperidino-1,2-propanediol, 3-pyrrolidino-1,2-propanediol,8-hydroxyjulolidine, 3-quinuclidinol, 3-tropanol, 1-methyl-2-pyrrolidineethanol, 1-aziridine ethanol, N-(2-hydroxyethyl)phthalimide, andN-(2-hydroxyethyl)isonicotinamide. Examples of suitable amidederivatives include formamide, N-methylformamide, N,N-dimethylformamide,acetamide, N-methylacetamide, N,N-dimethylacetamide, propionamide, andbenzamide. Suitable imide derivatives include phthalimide, succinimide,and maleimide.

Also useful are substituted ones of the hydroxyl group-bearingnitrogenous compounds in which some or all of the hydrogen atoms ofhydroxyl groups are replaced by methyl, ethyl, methoxymethyl,methoxyethoxymethyl, acetyl, or ethoxyethyl groups. Preferred aremethyl-, acetyl-, methoxymethyl- and methoxyethoxymethyl-substitutedcompounds of ethanolamine, diethanolamine and triethanolamine. Examplesinclude tris(2-methoxyethyl)amine, tris(2-ethoxyethyl)amine,tris(2-acetoxyethyl)amine, tris{2-(methoxymethoxy)ethyl}amine,tris{2-(methoxyethoxy)ethyl}amine,tris[2-{(2-methoxyethoxy)methoxy}ethyl]amine,tris{2-(2-methoxyethoxy)ethyl}amine,tris{2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine,tris{2-(1-ethoxypropoxy)ethyl}amine, andtris[2-{(2-hydroxyethoxy)ethoxy}ethyl]amine.

The basic compounds may be used alone or in admixture of two or more.The basic compound is preferably formulated in an amount of 0 to 2parts, and especially 0.01 to 1 part, per 100 parts by weight of thesolids in the resist composition. The use of more than 2 parts of thebasis compound would result in too low a sensitivity.

Illustrative, non-limiting, examples of the organic acid derivatives (E)include phenol, cresol, catechol, resorcinol, pyrogallol, fluoroglycin,bis(4-hydroxyphenyl)methane, 2,2-bis(4′-hydroxyphenyl)propane,bis(4-hydroxyphenyl)sulfone, 1,1,1-tris(4′-hydroxyphenyl)ethane,1,1,2-tris(4′-hydroxyphenyl)ethane, hydroxybenzophenone,4-hydroxyphenylacetic acid, 3-hydroxyphenylacetic acid,2-hydroxyphenylacetic acid, 3-(4-hydroxyphenyl)propionic acid,3-(2-hydroxyphenyl)propionic acid, 2,5-dihydroxyphenylacetic acid,3,4-dihydroxyphenylacetic acid, 1,2-phenylenediacetic acid,1,3-phenylenediacetic acid, 1,4-phenylenediacetic acid,1,2-phenylenedioxydiacetic acid, 1,4-phenylenedipropanoic acid, benzoicacid, salicylic acid, 4,4-bis(4′-hydroxyphenyl)valeric acid,4-tert-butoxyphenylacetic acid, 4-(4-hydroxyphenyl)butyric acid,3,4-dihydroxymandelic acid, and 4-hydroxymandelic acid. Of these,salicylic acid and 4,4-bis(41-hydroxyphenyl)valeric acid are preferred.They may be used alone or in admixture of two or more.

In the resist composition according to the invention, the organic acidderivative is preferably formulated in an amount of up to 5 parts, andespecially up to 1 part, per 100 parts by weight of the solids in theresist composition. The use of more than 5 parts of the organic acidderivative would result in too low a resolution. Depending on thecombination of the other components in the resist composition, theorganic acid derivative may be omitted.

In a chemical amplification, negative working, resist composition aswell, the onium salt of formula (1), (1a), (1a′) or (1b) according tothe invention may be used as the photoacid generator. This compositionfurther contains an alkali-soluble resin as component (H), examples ofwhich are intermediates of the above-described component (A) though notlimited thereto. Examples of the alkali-soluble resin includepoly(p-hydroxystyrene), poly(m-hydroxystyrene),poly(4-hydroxy-2-methylstyrene), poly(4-hydroxy-3-methylstyrene),poly(α-methyl-p-hydroxystyrene), partially hydrogenated p-hydroxystyrenecopolymers, p-hydroxystyrene-α-methyl-p-hydroxystyrene copolymers,p-hydroxystyrene-α-methylstyrene copolymers, p-hydroxystyrene-styrenecopolymers, p-hydroxystyrene-m-hydroxystyrene copolymers,p-hydroxystyrene-styrene copolymers, p-hydroxystyrene-acrylic acidcopolymers, p-hydroxystyrene-methacrylic acid copolymers,p-hydroxystyrene-methyl methacrylate copolymers,p-hydroxystyrene-acrylic acid-methyl methacrylate copolymers,p-hydroxystyrene-methyl acrylate copolymers,p-hydroxystyrene-methacrylic acid-methyl methacrylate copolymers,poly(methacrylic acid), poly(acrylic acid), acrylic acid-methyl acrylatecopolymers, methacrylic acid-methyl methacrylate copolymers, acrylicacid-maleimide copolymers, methacrylic acid-maleimide copolymers,p-hydroxystyreneacrylic acid-maleimide copolymers, andp-hydroxystyrenemethacrylic acid-maleimide copolymers, but are notlimited to these combinations.

Preferred are poly(p-hydroxystyrene), partially hydrogenatedp-hydroxystyrene copolymers, p-hydroxystyrenestyrene copolymers,p-hydroxystyrene-acrylic acid copolymers, andp-hydroxystyrene-methacrylic acid copolymers.

Alkali-soluble resins comprising units of the following formula (2) or(2′) are especially preferred.

Herein R⁴ is hydrogen or methyl, R⁵ is a straight, branched or cyclicalkyl group of 1 to 8 carbon atoms, x is 0 or a positive integer, y is apositive integer, satisfying x+y≦5, and M and N are positive integers,satisfying 0<N/(M+N)≦0.5.

The polymer should preferably have a weight average molecular weight(Mw) of 3,000 to 100,000. Many polymers with Mw of less than 3,000 donot perform well and are poor in heat resistance and film formation.Many polymers with Mw of more than 100,000 give rise to a problem withrespect to dissolution in the resist solvent and developer. The polymershould also preferably have a dispersity (Mw/Mn) of up to 3.5, and morepreferably up to 1.5. With a dispersity of more than 3.5, resolution islow in many cases. Although the preparation method is not critical, apoly(p-hydroxystyrene) or similar polymer with a low dispersity ornarrow dispersion can be synthesized by living anion polymerization.

To impart a certain function, suitable substituent groups may beintroduced into some of the phenolic hydroxyl and carboxyl groups on theabove mentioned polymer. Exemplary and preferred are substituent groupsfor improving adhesion to the substrate, substituent groups forimproving etching resistance, and especially substituent groups whichare relatively stable against acid and alkali and effective forcontrolling such that the dissolution rate in an alkali developer ofunexposed and low exposed areas of a resist film may not become toohigh. Illustrative, non-limiting, substituent groups include2-hydroxyethyl, 2-hydroxypropyl, methoxymethyl, methoxycarbonyl,ethoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl,4-methyl-2-oxo-4-oxoranyl, 4-methyl-2-oxo-4-oxanyl, methyl, ethyl,n-propyl, isopropyl, n-butyl, sec-butyl, acetyl, pivaloyl, adamantyl,isobornyl, and cyclohexyl. It is also possible to introduceacid-decomposable substituent groups such as t-butoxycarbonyl andrelatively acid-undecomposable substituent groups such as t-butyl andt-butoxycarbonylmethyl.

Also contained in the negative resist composition is (I) an acidcrosslinking agent capable of forming a crosslinked structure under theaction of an acid. Typical acid crosslinking agents are compounds havingat least two hydroxymethyl, alkoxymethyl, epoxy or vinyl ether groups ina molecule. Substituted glycoluril derivatives, urea derivatives, andhexa(methoxymethyl)melamine compounds are suitable as the acidcrosslinking agent in the chemically amplified, negative resistcomposition comprising the onium salt according to the invention.Examples include N,N,N′,N′-tetramethoxymethylurea,hexamethoxymethylmelamine, tetraalkoxymethyl-substituted glycolurilcompounds such as tetrahydroxymethyl-substituted glycoluril andtetramethoxymethylglycoluril, and condensates of phenolic compounds suchas substituted or unsubstituted bis(hydroxymethylphenol) compounds andbisphenol A with epichlorohydrin. Especially preferred acid crosslinkingagents are 1,3,5,7-tetraalkoxymethylglycolurils such as1,3,5,7-tetramethoxymethylglycoluril,1,3,5,7-tetrahydroxymethylglycoluril, 2,6-dihydroxymethyl-p-cresol,2,6-dihydroxymethylphenol, 2,2′,6,6′-tetrahydroxymethyl-bisphenol A,1,4-bis[2-(2-hydroxypropyl)]benzene, N,N,N′,N′-tetramethoxymethylurea,and hexamethoxymethylmelamine.

In the resist composition, an appropriate amount of the acidcrosslinking agent is about 1 to 25 parts, and especially about 5 to 15parts by weight per 100 parts by weight of the solids in thecomposition. The acid crosslinking agents may be used alone or inadmixture of two or more.

In the chemical amplification type, negative working, resistcomposition, an alkali-soluble compound having a molecular weight of upto 2,500 may be blended. The compound should preferably have at leasttwo phenol and/or carboxyl groups. Illustrative, non-limiting, examplesinclude cresol, catechol, resorcinol, pyrogallol, fluoroglycin,bis(4-hydroxyphenyl)methane, 2,2-bis(4′-hydroxyphenyl)propane,bis(4-hydroxyphenyl)sulfone, 1,1,1-tris(4′-hydroxyphenyl)ethane,1,1,2-tris(4′-hydroxyphenyl)ethane, hydroxybenzophenone,4-hydroxyphenylacetic acid, 3-hydroxyphenylacetic acid,2-hydroxyphenylacetic acid, 3-(4-hydroxyphenyl)propionic acid,3-(2-hydroxyphenyl)propionic acid, 2,5-dihydroxyphenylacetic acid,3,4-dihydroxyphenylacetic acid, 1,2-phenylenediacetic acid,1,3-phenylenediacetic acid, 1,4-phenylenediacetic acid,1,2-phenylenedioxydiacetic acid, 1,4-phenylenedipropanoic acid, benzoicacid, salicylic acid, 4,4-bis(4′-hydroxyphenyl)valeric acid,4-tert-butoxyphenylacetic acid, 4-(4-hydroxyphenyl)butyric acid,3,4-dihydroxymandelic acid, and 4-hydroxymandelic acid. Of these,salicylic acid and 4,4-bis(4′-hydroxyphenyl)valeric acid are preferred.They may be used alone or in admixture of two or more. The additionamount is 0 to 20 parts, preferably 2 to 10 parts by weight per 100parts by weight of the solids in the composition although it is notcritical.

In the resist composition according to the invention, there may be addedsuch additives as a surfactant for improving coating, and a lightabsorbing agent for reducing diffuse reflection from the substrate.

Illustrative, non-limiting, examples of the surfactant include nonionicsurfactants, for example, polyoxyethylene alkyl ethers such aspolyoxyethylene lauryl ether, polyoxyethylene stearyl ether,polyoxyethylene cetyl ether, and polyoxyethylene oleyl ether,polyoxyethylene alkylaryl ethers such as polyoxyethylene octylphenolether and polyoxyethylene nonylphenol ether, polyoxyethylenepolyoxypropylene block copolymers, sorbitan fatty acid esters such assorbitan monolaurate, sorbitan monopalmitate, and sorbitan monostearate,and polyoxyethylene sorbitan fatty acid esters such as polyoxyethylenesorbitan monolaurate, polyoxyethylene sorbitan monopalmitate,polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitantrioleate, and polyoxyethylene sorbitan tristearate; fluorochemicalsurfactants such as EFTOP EF301, EF303 and EF342 (Tohkem Products K.K.),Megaface F171, F172 and F173 (Dai-Nippon Ink & Chemicals K.K.), FloradeFC430 and FC431, (Sumitomo 3M K.K.), Aashiguard AG710, Surflon S-381,S-382, SC101, SC102, SC103, SC104, SC105, SC106, Surfynol E1004, KH-10,KH-20, KH-30 and KH-40 (Asahi Glass K.K.); organosiloxane polymersKP341, X-70-092 and X-70-093 (Shin-Etsu Chemical Co., Ltd.), acrylicacid or methacrylic acid Polyflow No. 75 and No. 95 (Kyoeisha UshiKagaku Kogyo K.K.). Inter alia, FC430, Surflon S-381 and Surfynol E1004are preferred. These surfactants may be used alone or in admixture.

In the resist composition according to the invention, the surfactant ispreferably formulated in an amount of up to 2 parts, and especially upto 1 part, per 100 parts by weight of the solids in the resistcomposition.

In the resist composition according to the invention, a UV absorber maybe added.

Exemplary UV absorbers are fused polycyclic hydrocarbon derivatives suchas pentalene, indene, naphthalene, azulene, heptalene, biphenylene,indacene, fluorene, phenalene, phenanthrene, anthracene, fluoranthene,acephenanthrylene, aceanthrylene, triphenylene, pyrene, chrysene,pleiadene, picene, perylene, pentaphene, pentacene, benzophenanthrene,anthraquinone, anthrone, benzanthrone, 2,7-dimethoxynaphthalene,2-ethyl-9,10-dimethoxyanthracene, 9,10-dimethylanthracene,9-ethoxyanthracene, 1,2-naphthoquinone, 9-fluorene, and compounds of thefollowing formulae (D1) and (D2); fused heterocyclic derivatives such asthioxanthen-9-one, thianthrene, dibenzothiophene; benzophenonederivatives such as 2,3,4-trihydroxybenzophenone,2,3,4,4′-tetrahydroxybenzophenone, 2,4-dihydroxybenzophenone,3,5-dihydroxybenzophenone, 4,4′-dihydroxybenzophenone, and4,4′-bis(dimethylamino)benzophenone; squalic acid derivatives such assqualic acid and dimethyl squalate; diaryl sulfoxide derivatives such asbis(4-hydroxyphenyl) sulfoxide, bis(4-tert-butoxyphenyl) sulfoxide,bis(4-tert-butoxycarbonyloxyphenyl) sulfoxide, andbis[4-(1-ethoxyethoxy)phenyl]sulfoxide; diarylsulfone derivatives suchas bis(4-hydroxyphenyl)sulfone, bis(4-tert-butoxyphenyl)sulfone,bis(4-tert-butoxycarbonyloxyphenyl)sulfone,bis[4-(1-ethoxyethoxy)phenyl]sulfone, andbis[4-(1-ethoxypropoxy)phenyl]sulfone; diazo compounds such asbenzoquinonediazide, naphthoquinonediazide, anthraquinonediazide,diazofluorene, diazotetralone, and diazophenanthrone; quinonediazidegroup-containing compounds such as complete or partial ester compoundsbetween naphthoquinone-1,2-diazide-5-sulfonic acid chloride and2,3,4-trihydroxybenzophenone and complete or partial ester compoundsbetween naphthoquinone-1,2-diazide-4-sulfonic acid chloride and2,4,4′-trihydroxybenzophenone; tert-butyl 9-anthracenecarboxylate,tert-amyl 9-anthracenecarboxylate, tert-methoxymethyl9-anthracenecarboxylate, tert-ethoxyethyl 9-anthracenecarboxylate,2-tert-tetrahydropyranyl 9-anthracenecarboxylate, and2-tert-tetrahydrofuranyl 9-anthracenecarboxylate.

Herein, R⁶¹ to R⁶³ are independently hydrogen or a straight or branchedalkyl, straight or branched alkoxy, straight or branched alkoxyalkyl,straight or branched alkenyl or aryl group. R⁶⁴ is a substituted orunsubstituted divalent aliphatic hydrocarbon group which may contain anoxygen atom, a substituted or unsubstituted divalent alicyclichydrocarbon group which may contain an oxygen atom, a substituted orunsubstituted divalent aromatic hydrocarbon group which may contain anoxygen atom, or an oxygen atom. R⁶⁵ is an acid labile group as describedabove. Letter J is equal to 0 or 1, E, F and G are 0 or integers of 1 to9, H is a positive integer of 1 to 10, satisfying E+F+G+H≦10.

An appropriate amount of UV absorber blended is 0 to 10 parts, morepreferably 0.5 to 10 parts, most preferably 1 to 5 parts by weight per100 parts by weight of the base resin.

For the microfabrication of integrated circuits, any well-knownlithography may be used to form a resist pattern from the chemicalamplification, positive or negative working, resist compositionaccording to the invention.

The composition is applied onto a substrate (e.g., Si, SiO₂, SiN, SiON,TiN, WSi, BPSG, SOG, organic anti-reflecting film, etc.) by a suitablecoating technique such as spin coating, roll coating, flow coating, dipcoating, spray coating or doctor coating. The coating is prebaked on ahot plate at a temperature of 60 to 150° C. for about 1 to 10 minutes,preferably 80 to 120° C. for 1 to 5 minutes. The resulting resist filmis generally 0.1 to 2.0 μm thick. With a mask having a desired patternplaced above the resist film, the resist film is then exposed to actinicradiation, preferably having an exposure wavelength of up to 300 nm,such as UV, deep-UV, electron beams, x-rays, excimer laser, γ-rays andsynchrotron radiation in an exposure dose of about 1 to 200 mJ/cm²,preferably about 10 to 100 mJ/cm². The film is further baked on a hotplate at 60 to 150° C. for 1 to 5 minutes, preferably 80 to 120° C. for1 to 3 minutes (post-exposure baking=PEB).

Thereafter the resist film is developed with a developer in the form ofan aqueous base solution, for example, 0.1 to 5%, preferably 2 to 3%aqueous solution of tetramethylammonium hydroxide (TMAH) for 0.1 to 3minutes, preferably 0.5 to 2 minutes by conventional techniques such asdipping, puddling or spraying. In this way, a desired resist pattern isformed on the substrate. It is appreciated that the resist compositionof the invention is best suited for micro-patterning using such actinicradiation as deep UV with a wavelength of 254 to 193 nm, vacuum UV witha wavelength of 157 nm, electron beams, x-rays, excimer laser, γ-raysand synchrotron radiation. With any of the above-described parametersoutside the above-described range, the process may sometimes fail toproduce the desired pattern.

EXAMPLE

Examples of the invention are given below by way of illustration and notby way of limitation.

Synthesis Example 1 Synthesis of sodium4-(4′-methylphenylsulfonyloxy)benzenesulfonate

In 400 g of tetrahydrofuran and 250 g of water were dissolved 208 g of4-phenolsulfonic acid hydrate and 191 g (1.0 mol) of p-toluenesulfonylchloride. With stirring under ice cooling, 80 g (2.0 mol) of sodiumhydroxide in 125 g of water was added dropwise at such a rate that thetemperature might not exceed 20° C. After the completion of addition,the reaction solution was ripened for 2 hours at room temperature. Tothe reaction solution, 700 g of dichloromethane was added whereuponsodium 4-(4′-methylphenylsulfonyloxy)benzenesulfonate crystallized. Thecrystals were collected by filtration and washed with 200 g ofdichloromethane. The yield was 370 g (not dried).

Synthesis Example 2 Synthesis of triphenylsulfonium chloride

In 1,600 g of dichloromethane was dissolved 161 g (0.8 mol) of diphenylsulfoxide. With stirring under ice cooling, 260 g (2.4 mol) oftrimethylsilyl chloride was added dropwise at such a rate that thetemperature might not exceed 20° C. The reaction solution was ripenedunder ice cool for 30 minutes. Then, the Grignard reagent which wasprepared from 58 g (2.4 mol) of metallic magnesium, 270 g (2.4 mol) ofchlorobenzene and 672 g of THF was added dropwise at such a rate thatthe temperature might not exceed 20° C. The reaction solution wasripened for one hour. Below 20° C., 50 g of water was added to thereaction solution for terminating the reaction. Further, 600 g of water,40 g of 12N hydrochloric acid and 1,000 g of diethyl ether were added tothe solution.

The aqueous layer was separated and washed with 300 g of diethyl ether,obtaining an aqueous solution of triphenylsulfonium chloride. Thisaqueous solution was subject to the subsequent reaction without furtherpurification.

Synthesis Example 3 Synthesis of triphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate

The sodium 4-(4′-methylphenylsulfonyloxy)benzenesulfonate crude productobtained in Synthesis Example 1, 370 g, was added to the aqueoustriphenylsulfonium chloride solution obtained in Synthesis Example 2 and900 g of dichloromethane, which was stirred for one hour at roomtemperature. The organic layer was separated, washed with 800 g ofwater, and concentrated in vacuum. To 280 g of the residue, 800 g ofdiethyl ether was added for crystallization. The crystals were collectedby filtration and washed with 300 g of diethyl ether, obtaining 262 g(yield 74%) of the end product, triphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate.

The thus obtained triphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate was analyzed by nuclearmagnetic resonance (NMR) spectroscopy, infrared (IR) absorptionspectroscopy, and elemental analysis, with the results shown below.

¹H-NMR: CDCl₃, ppm

(1) Ha 2.39 singlet 3H (2) Hd 6.81-6.84 doublet 2H (3) Hb 7.22-7.26doublet 2H (4) Hc, He, Hf 7.58-7.84 multiplet 19H

IR: cm⁻¹ 3057, 3054, 1591, 1483, 1477, 1442, 1367, 1294, 1213, 1186,1169, 1151, 1124, 1093, 1032, 1012, 863, 825, 759

Elemental analysis for C₃₁H₂₆O₆S₃: % Calcd.: C, 63.0; H, 4.4. Found: C,62.5; H, 4.5.

Synthesis Example 4 Synthesis of sodiumphenylsulfonyloxybenzenesulfonate

The end product was synthesized as in Synthesis Example 1 except thatphenylsulfonyl chloride was used instead of the toluenesulfonylchloride.

Synthesis Example 5 Synthesis of sodium4-(10′-camphorsulfonyloxy)benzenesulfonate

The end product was synthesized as in Synthesis Example 1 except that10-camphorsulfonyl chloride was used instead of the toluenesulfonylchloride.

Synthesis Example 6 Synthesis of 4-tert-butylphenyldiphenylsulfoniumchloride

The end product was synthesized as in Synthesis Example 2 except that4-tert-butylchlorobenzene was used instead of the chlorobenzene.

Synthesis Example 7 Synthesis of 4-tert-butoxyphenyldiphenylsulfoniumchloride

The end product was synthesized as in Synthesis Example 2 except that4-tert-butoxychlorobenzene was used instead of the chlorobenzene anddichloromethane containing 5 wt % triethylamine was used as solvents.

Synthesis Example 8 Synthesis of bis(4-tert-butylphenyl)iodoniumhydrogen sulfate

While a mixture of 168 g (1.0 mol) of tert-butylbenzene, 107 g (0.5 mol)of potassium iodate (KIO₃) and 100 g of acetic anhydride was stirredunder ice cooling, a mixture of 70 g of acetic anhydride and 190 g ofconc. sulfuric acid was added dropwise at such a rate that thetemperature might not exceed 30° C. The reaction solution was ripenedfor 3 hours at room temperature. The solution was ice cooled again and500 g of water was added dropwise for terminating the reaction. Thereaction solution was extracted with 800 g of dichloromethane. Sodiumhydrogen sulfite, 12 g, was added to the organic layer for decoloring.The organic layer was washed three times with 500 g of water. The washedorganic layer was concentrated in vacuum, obtaining the crude endproduct. This product was subject to the subsequent reaction withoutfurther purification.

Synthesis Example 9 Synthesis of bis(4-tert-butylphenyl)iodonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate

The end product was obtained as in Synthesis Example 3 except thatbis(4-tert-butylphenyl)iodonium hydrogen sulfate obtained in SynthesisExample 8 and 1,000 g of water were used instead of thetriphenylsulfonium chloride in Synthesis Example 3.

The thus obtained bis(4-tert-butylphenyl)iodonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate was analyzed by NMRspectroscopy, IR spectroscopy, and elemental analysis, with the resultsshown below.

¹H-NMR: CDCl₃, ppm

(1) Ha 2.41 singlet 3H (2) Hc 7.63-7.66 doublet 2H (3) Hb 7.26-7.29doublet 2H (4) He 7.46-7.49 doublet 2H (5) Hd 6.79-6.82 doublet 2H (6)Hf 1.26 singlet 18H (7) Hi 7.80-7.84 doublet 4H (8) Hg 7.34-7.37 doublet4H

IR: cm⁻¹ 3442, 3057, 2964, 2906, 2870, 1628, 1597, 1591, 1484, 1462,1396, 1377, 1294, 1225, 1198, 1182, 1155, 1120, 1093, 1057, 1030, 1009,995, 863, 820, 759, 715, 682, 665, 633, 609

Elemental analysis for C₃₃H₃₇IO₆S₂: % Calcd.: C, 55.0; H, 5.2. Found: C,55.1; H, 5.1.

Synthesis Example 10 Synthesis of (4-tert-butoxyphenyl)diphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate

The end product was obtained as in Synthesis Example 3 except that(4-tert-butoxyphenyl)diphenylsulfonium chloride obtained in SynthesisExample 7 were used instead of the triphenylsulfonium chloride.

The thus obtained (4-tert-butoxyphenyl)diphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate was analyzed by NMRspectroscopy, IR spectroscopy, and elemental analysis, with the resultsshown below.

¹H-NMR; CDCl₃, ppm

(1) Ha 2.35 singlet 3H (2) Hb 7.26-7.29 doublet 2H (4) He 7.46-7.49doublet 2H (5) Hd 6.77-6.80 doublet 2H (6) Hf 1.38 singlet 9H (7) Hg7.12-7.15 doublet 2H (8) Hc, Hi, Hj 7.34-7.37 multiplet 14H

IR: cm⁻¹ 3435, 3061, 2980, 2935, 2873, 1585, 1487, 1446, 1396, 1371,1308, 1265, 1198, 1155, 1120, 1093, 1070, 1032, 1012, 928, 867, 816,758, 685, 656, 652, 633, 611

Elemental analysis for C₃₅H₃₄O₇S₃: % Calcd.: C, 63.4; H, 5.2. Found: C,63.3; H, 5.2.

Synthesis Example 11 Synthesis of (4-tert-butylphenyl)diphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate

The end product was obtained as in Synthesis Example 3 except that4-tert-butylphenyldiphenylsulfonium chloride obtained in SynthesisExample 6 was used instead of the triphenylsulfonium chloride inSynthesis Example 3.

The thus obtained (4-tert-butylphenyl)diphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate was analyzed by NMRspectroscopy, IR spectroscopy, and elemental analysis, with the resultsshown below.

¹H-NMR: CDCl₃, ppm

(1) Ha 2.41 singlet 3H (2) Hb 7.26-7.27 doublet 2H (4) He 7.83-7.86doublet 2H (5) Hd 6.84-6.87 doublet 2H (6) Hf 1.31 singlet 9H (7) Hc,Hg, Hi, Hj 7.62-7.67 multiplet 16H

IR: cm⁻¹ 3543, 3466, 3084, 3053, 2962, 2906, 2870, 1589, 1487 1477,1446, 1396, 1373, 1294, 1269, 1221, 1213, 1198, 1178, 1155, 1120, 1093,1070, 1032, 1012, 868, 816, 756, 685, 656, 632, 611

Elemental analysis for C₃₅H₃₄O₆S₃: %

Calcd.: C, 65.0; H, 5.3. Found: C, 65.0; H, 5.2.

Synthesis Example 12 Synthesis of (4-methylphenyl)diphenylsulfoniumchloride

The end product was synthesized as in Synthesis Example 2 except that4-chlorotoluene was used instead of the chlorobenzene.

Synthesis Example 13 Synthesis of (4-methylphenyl)diphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate

The end product was obtained as in Synthesis Example 3 except that4-methylphenyldiphenylsulfonium chloride obtained in Synthesis Example12 was used instead of the triphenylsulfonium chloride in SynthesisExample 3.

The thus obtained (4-methylphenyl)diphenylsulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate was analyzed by NMRspectroscopy, IR spectroscopy, and elemental analysis, with the resultsshown below.

¹H-NMR: CDCl₃, ppm

(1) Ha 2.42 singlet 3H (2) Hb 7.23-7.26 doublet 2H (4) Hc 7.78-7.81doublet 2H (5) Hd 6.80-6.85 doublet 2H (6) Hf 2.39 singlet 3H (7) Hg7.41-7.44 doublet 2H (8) He, Hi, Hj 7.59-7.73 multiplet 14H

IR: cm⁻¹ 3435, 3055, 1591, 1484, 1477, 1446, 1369, 1311, 1294, 1223,1209, 1198, 1182, 1171, 1153, 1120, 1093, 1068, 1034, 1013, 862, 823,808, 762, 685, 656, 633, 613

Elemental analysis for C₃₂H₂₈O₆S₃: % Calcd.: C, 63.6; H, 4.7. Found: C,63.5; H, 4.9.

Synthesis Example 14 Synthesis of tris(4-methylphenyl)sulfonium chloride

The end product was synthesized as in Synthesis Example 2 except thatbis(4-methylphenyl)sulfoxide was used instead of the phenyl sulfoxideand 4-chlorotoluene was used instead of the chlorobenzene.

Synthesis Example 15 Synthesis of tris(4-methylphenyl)sulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate

The end product was obtained as in Synthesis Example 3 except thattris(4-methylphenyl)sulfonium chloride obtained in Synthesis Example 14was used instead of the triphenylsulfonium chloride in Synthesis Example3.

The thus obtained tris(4-methylphenyl)sulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate was analyzed by NMRspectroscopy, IR spectroscopy, and elemental analysis, with the resultsshown below.

¹H-NMR: CDCl₃, ppm

(1) Ha 2.41 singlet 3H (2) Hb 7.25-7.27 doublet 2H (4) Hc 7.83-7.86doublet 2H (5) Hd 6.84-6.87 doublet 2H (6) Hf 2.39 singlet 9H (7) He,Hg, Hi 7.62-7.67 multiplet 14H

IR: cm⁻¹ 3440, 3084, 3043, 2953, 2924, 2871, 1630, 1591, 1487, 1452,1402, 1371, 1315, 1296, 1198, 1155, 1120, 1092, 1072, 1032, 1013, 862,814, 760, 729, 685, 656, 633, 613

Elemental analysis for C₃₄H₃₂O₆S₃: % Calcd.: C, 64.5; H, 5.1. Found: C,64.3; H, 5.2.

Synthesis Example 16 Synthesis of tris(4-tert-butylphenyl)sulfoniumchloride

The end product was synthesized as in Synthesis Example 2 except thatbis(4-tert-butylphenyl)sulfoxide was used instead of the phenylsulfoxide and 4-tert-butylchlorobenzene was used instead of thechlorobenzene.

Synthesis Example 17 Synthesis of tris(4-tert-butylphenyl)sulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate

The end product was obtained as in Synthesis Example 3 except thattris(4-tert-butylphenyl)sulfonium chloride obtained in Synthesis Example16 was used instead of the triphenylsulfonium chloride in SynthesisExample 3.

The thus obtained tris(4-tert-butylphenyl)sulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate was analyzed by NMRspectroscopy, IR spectroscopy, and elemental analysis, with the resultsshown below.

¹H-NMR: CDCl₃, ppm

(1) Ha 2.40 singlet 3H (2) Hb 7.25-7.27 doublet 2H (4) Hc 7.83-7.86doublet 2H (5) Hd 6.84-6.87 doublet 2H (6) Hf 1.31 singlet 27H (7) He,Hg, Hi 7.62-7.67 multiplet 14H

IR: cm⁻¹ 3440, 3059, 2964, 2906, 2870, 1626, 1589, 1487, 1464, 1400,1377, 1294, 1269, 1198, 1173, 1155, 1120, 1093, 1072, 1032, 1012, 862,762, 727, 704, 683, 656, 633, 611

Elemental analysis for C₄₃H₅₀O₆S₃: Calcd.: C, 68.0; H, 6.6. Found: C,68.0; H, 6.8.

Synthesis Example 18 Synthesis of 4-tert-butylphenyldiphenylsulfonium4-(10′-camphorsulfonyloxy)benzenesulfonate

The end product was synthesized as in Synthesis Example 3 except that4-tert-butylphenyldiphenylsulfonium chloride was used instead of thetriphenylsulfonium chloride and sodium4-(10′-camphorsulfonyloxy)benzenesulfonate was used instead of thesodium 4-(4′-methylphenylsulfonyloxy)benzenesulfonate.

Synthesis Example 19 Synthesis of 4-tert-butoxyphenyldiphenylsulfoniumbenzenesulfonyloxybenzenesulfonate

The end product was synthesized as in Synthesis Example 10 except that4-tert-butoxyphenyldiphenylsulfonium chloride and sodiumbenzenesulfonyloxybenzenesulfonate were used.

Synthesis Example 20 Synthesis of sodium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate

The end product was synthesized as in Synthesis Example 1 except that1.0 mole of potassium hydroquinonesulfonate and 2.5 mole ofp-toluenesulfonic acid chloride were used.

Synthesis Example 21 Synthesis of triphenylsulfonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate

The end product was obtained as in Synthesis Example 3 except thatsodium 2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate obtained inSynthesis Example 20 was used.

The thus obtained triphenylsulfonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate was analyzed by NMRspectroscopy, IR spectroscopy, and elemental analysis, with the resultsshown below.

¹H-NMR: CDCl₃, ppm

(1) Ha or Ha′ 2.30 singlet 3H (2) Ha′ or Ha 2.37 singlet 3H (3) Hb orHb′ 7.16-7.19 doublet 2H (4) Hb′ or Hb 7.21-7.23 doublet 2H (5) Hc′7.98-8.01 doublet 2H (6) Hc, Hd, Hg, Hh, Hi 7.58-7.72 multiplet 18H (7)He 6.98-7.02 quadruplet 1H (8) Hf 7.33-7.36 doublet 1H

IR: cm⁻¹ 3442, 3088, 3061, 2922, 1921, 1728, 1597, 1468, 1448, 1398,1371, 1294, 1238, 1224, 1196, 1176, 1157, 1128, 1090, 1080, 1026, 997,912, 862, 816, 750, 708

Elemental analysis for C₃₈H₃₂O₉S₄: % Calcd.: C, 60.0; H, 4.2. Found: C,59.8; H, 4.1.

Synthesis Example 22 Synthesis of bis(4-tert-butylphenyl)iodonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate

The end product was obtained as in Synthesis Example 9 except thatsodium 2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate obtained inSynthesis Example 20 was used.

The thus obtained bis(4-tert-butylphenyl)iodonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate was analyzed by NMRspectroscopy, IR spectroscopy, and elemental analysis, with the resultsshown below.

¹H-NMR: CDCl₃, ppm

(1) Ha or Ha′ 2.33 singlet 3H (2) Ha′ or Ha 2.39 singlet 3H (3) Hb, Hb′7.22-7.25 doublet 4H (4) Hc 7.59-7.62 doublet 2H (5) Hc′ 7.94-7.97doublet 2H (6) Hd 7.49-7.50 doublet 1H (7) He 6.98-7.02 quadruplet 1H(8) Hf, Hh 7.37-7.44 multiplet 5H (9) Hg 1.26 singlet 18H (10) Hi7.84-7.89 doublet 4H

IR: cm⁻¹ 3059, 2964, 2906, 2870, 1919, 1597, 1470, 1396, 1369, 1286,1246, 1194, 1176, 1157, 1128, 1090, 1080, 1022, 993, 912, 864, 818, 768,737, 708

Elemental analysis for C₄₀H₄₃IO₉S₃: % Calcd.: C, 53.9; H, 4.9. Found: C,54.0; H, 4.8.

Synthesis Example 23 Synthesis of tris(4-methylphenyl)sulfonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate

The end product was obtained as in Synthesis Example 15 except thatsodium 2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate obtained inSynthesis Example 20 was used.

The thus obtained tris(4-methylphenyl)sulfonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate was analyzed by NMRspectroscopy, IR spectroscopy, and elemental analysis, with the resultsshown below.

¹H-NMR: CDCl₃, ppm

(1) Ha or Ha′ 2.33 singlet 3H (2) Ha′ or Ha 2.39 singlet 3H (3) Hb orHb′ 7.18-7.21 doublet 2H (4) Hb′ or Hb 7.22-7.25 doublet 2H (5) Hc′8.05-8.08 doublet 2H (6) Hd 7.64-7.65 singlet 1H (7) He 6.86-6.91quadruplet 1H (8) Hf, Hh 7.38-7.43 multiplet 7H (9) Hg 2.40 singlet 9H(10) Hc, Hi 7.56-7.60 multiplet 8H

IR: cm⁻¹ 3442, 3086, 3047, 2976, 2958, 2922, 2870, 1593, 1493, 1468,1400, 1369, 1292, 1228, 1194, 1176, 1155, 1126, 1087, 1080, 1026, 912,864, 814, 769, 740, 708

Elemental analysis for C₄₁H₃₈O₉S₄: % Calcd.: C, 61.3; H, 4.8. Found: C,61.4; H, 4.8.

Synthesis Example 24 Synthesis of tris(4-tert-butylphenyl)sulfonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate

The end product was obtained as in Synthesis Example 17 except thatsodium 2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate obtained inSynthesis Example 20 was used.

The thus obtained tris(4-tert-butylphenyl)sulfonium2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate was analyzed by NMRspectroscopy, IR spectroscopy, and elemental analysis, with the resultsshown below.

¹H-NMR: CDCl₃, ppm

(1) Ha or Ha′ 2.35 singlet 3H (2) Ha′ or Ha 2.40 singlet 3H (3) Hb orHb′ 7.19-7.22 doublet 2H (4) Hb′ or Hb 7.22-7.25 doublet 2H (5) Hc′8.06-8.09 doublet 2H (6) Hc, Hh 7.59-7.65 multiplet 8H (7) Hd, Hi7.65-7.70 multiplet 7H (7) He 6.89-6.94 quadruplet 1H (8) Hf 7.42-7.45doublet 1H (9) Hg 1.26 singlet 27H

IR: cm⁻¹ 3440, 3091, 3061, 2964, 2906, 2870, 1921, 1732, 1632, 1597,1491, 1468, 1400, 1367, 1292, 1242, 1227, 1196, 1176, 1157, 1128, 1090,1080, 1026, 1007, 912, 862, 818, 769, 739, 708

Elemental analysis for C₅₀H₅₆O₉S₄: % Calcd.: C, 64.6; H, 6.1. Found: C,64.7; H, 6.0.

Examples 1-24 and Comparative Examples 1-3

Resist materials were formulated in accordance with the formulationshown in Tables 1 to 3. The components used are shown below.

Polymer A: poly(p-hydroxystyrene) in which hydroxyl groups are protectedwith 15 mol % of 1-ethoxyethyl groups and 15 mol % oftert-butoxycarbonyl groups, having a weight average molecular weight of12,000.

Polymer B: poly(p-hydroxystyrene) in which hydroxyl groups are protectedwith 10 mol % of 1-ethoxyethyl groups and 15 mol % oftert-butoxycarbonyl groups, having a weight average molecular weight of11,000.

Polymer C: poly(p-hydroxystyrene) in which hydroxyl groups are protectedwith 15 mol % of 1-ethoxyethyl groups and 10 mol % oftert-butoxycarbonyl groups, having a weight average molecular weight of11,000.

Polymer D: poly(p-hydroxystyrene) in which hydroxyl groups are protectedwith 25 mol % of 1-ethoxyethyl groups and crosslinked with 3 mol % of1,2-propanediol divinyl ether, having a weight average molecular weightof 13,000.

Polymer E: poly(p-hydroxystyrene) in which hydroxyl groups are protectedwith 30 mol % of 1-ethoxyethyl groups, having a weight average molecularweight of 12,000.

Polymer F: poly(p-hydroxystyrene) in which hydroxyl groups are protectedwith 10 mol % of 1-ethoxyethyl groups and 3 mol % of tert-butoxycarbonylgroups, and crosslinked with 3 mol % of 1,2-propanediol divinyl ether,having a weight average molecular weight of 15,000.

Polymer G: poly(p-hydroxystyrene) in which hydroxyl groups are protectedwith 15 mol % of 1-ethoxyethyl groups and 10 mol % oftert-butoxycarbonyl groups, and crosslinked with 3 mol % of1,2-propanediol divinyl ether, having a weight average molecular weightof 13,000.

Polymer H: p-hydroxystyrene-l-ethylcyclopentyl methacrylate copolymerhaving a compositional ratio (molar ratio) of 70:30 and a weight averagemolecular weight of 11,000.

Polymer I: p-hydroxystyrene-l-ethylcyclopentyl acrylate copolymer havinga compositional ratio (molar ratio) of 65:35 and a weight averagemolecular weight of 14,000.

Polymer J: the same as Polymer G, but further containing 5% by weight ofstyrene and having a weight average molecular weight of 12,000.

Polymer K: p-hydroxystyrene-1-ethylcyclopentyl methacrylate copolymerhaving a compositional ratio (molar ratio) of 70:30 in which phenolichydroxyl groups on p-hydroxystyrene are crosslinked with 2 mol % of1,2-propanediol divinyl ether, and having a weight average molecularweight of 13,000.

Polymer L: p-hydroxystyrene-1-ethylcyclopentylmethacrylate-p-tert-butoxystyrene copolymer having a compositional ratio(molar ratio) of 60:30:10 and a weight average molecular weight of12,000.

Polymer M: p-hydroxystyrene-1-ethylcyclopentylmethacrylate-p-tert-butoxycarbonyloxystyrene copolymer having acompositional ratio (molar ratio) of 70:20:10 in which phenolic hydroxylgroups on p-hydroxystyrene are crosslinked with 1 mol % of1,2-propanediol divinyl ether, and having a weight average molecularweight of 12,000.

Polymer N: poly(p-hydroxystyrene) in which hydroxyl groups are protectedwith 8 mol % of acetyl groups, having a weight average molecular weightof 8,000.

PAG1: triphenylsulfonium 4-(4′-methylphenylsulfonyloxy)benzenesulfonate

PAG2: tris(4-tert-butylphenyl)sulfonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate

PAG3: bis(4-tert-butylphenyl)iodonium4-(4′-methylphenylsulfonyloxy)benzenesulfonate

PAG4: (4-tert-butoxyphenyl)diphenylsulfonium p-toluene-sulfonate

PAG5: (4-tert-butoxyphenyl)diphenylsulfonium 10-camphor-sulfonate

PAG6: bis(tert-butylsulfonyl)diazomethane

PAG7: bis(cyclohexylsulfonyl)diazomethane

PAG8: bis(2,4-dimethylphenylsulfonyl)diazomethane

PAG9: N-10-camphorsulfonyloxysuccinimide

Crosslinker A: 1,3,5,7-tetramethoxymethylglycoluril

Dissolution inhibitor A: bis(4-(2′-tetrahydropyranyloxy)phenyl)methane

Basic compound A: tri-n-butylamine

Basic compound B: tris(2-methoxyethyl)amine

Organic acid derivative A: 4,4-bis(4′-hydroxyphenyl)valeric acid

Organic acid derivative B: salicylic acid

Surfactant A: FC-430 (Sumitomo 3M K.K.)

Surfactant B: Surflon S-381 (Asahi Glass K.K.)

UV absorber A: 9,10-dimethylanthracene

Solvent A: propylene glycol methyl ether acetate

Solvent B: ethyl lactate

The resist materials thus obtained were each filtered through a 0.2-μmTeflon filter, thereby giving resist solutions. These resist solutionswere spin-coated onto silicon wafers, then baked at 100° C. for 90seconds on a hot plate to give resist films having a thickness of 0.6μm. The resist films were exposed using an excimer laser stepperNSR2005EX (Nikon K.K., NA 0.5), through a photomask having apredetermined pattern, then baked (PEB) at 110° C. for 90 seconds, anddeveloped with a solution of 2.38% tetramethylammonium hydroxide inwater, thereby giving positive patterns (Examples 1 to 23 andComparative Examples 1-3) or negative patterns (Example 24).

The resulting resist patterns were evaluated as described below.

Resist Pattern Evaluation

Provided that the exposure dose which provides a 1:1 resolution at thetop and bottom of a 0.24-μm line-and-space pattern was the optimumexposure dose (sensitivity Eop), the minimum line width of aline-and-space pattern which was ascertained separate at this dose wasthe resolution of a test resist. The shape in cross section of theresolved resist pattern was examined under a scanning electronmicroscope.

The PED stability of a resist was evaluated by effecting post-exposurebake (PED) after 24 hours of holding from exposure at the optimum doseand determining a variation in line width (or groove width for thenegative resist). The less the variation, the greater is the PEDstability.

The results of resist pattern evaluation are shown in Table 4.

Other Evaluation

The solubility of resist material in a solvent mixture was examined byvisual observation and in terms of clogging upon filtration.

With respect to the applicability of a resist solution, uneven coatingwas visually observed. Additionally, using a film gage Clean Track Mark8 (Tokyo Electron K.K.), the thickness of a resist film on a commonwafer was measured at different positions, based on which a variationfrom the desired coating thickness (0.6 μm) was calculated. Theapplicability was rated “good” when the variation was within 0.5% (thatis, within 0.003 μm), “unacceptable” when the variation was from morethan 0.5% to 1%, and “poor” when the variation was more than 1%.

Storage stability was judged in terms of particle formation orsensitivity change during aging. After the resist solution was aged for100 days at the longest, the number of particles of greater than 0.3 μmper ml of the resist solution was counted by means of a particle counterKL-20A (Rion K.K.), and the particle formation was determined “good”when the number of particles is not more than 5. Also, the sensitivitychange was rated “good” when a change with time of sensitivity (Eop) waswithin 5% from that immediately after preparation, and “poor” when thechange is more than 5%.

Defect appearing on the developed pattern was observed under a scanningelectron microscope (TDSEM) model S-7280H (Hitachi K.K.). The resistfilm was rated “good” when the number of defect was up to 10 per 100μM², “unacceptable” when from 11 to 15, and “poor” when more than 15.

Defect (residue) left after resist stripping was examined using asurface scanner Surf-Scan 6220 (Tencol Instruments). A resist-coated8-inch wafer was subjected to entire exposure rather than patternedexposure, processed in a conventional manner, and developed with a 2.38%TMAH solution before the resist film was peeled off (only the resistfilm in the exposed area was stripped). After the resist film wasstripped, the wafer was examined and rated “good” when the number ofdefect of greater than 0.20 μm was up to 100, “unacceptable” when from101 to 150, and “poor” when more than 150.

The results are shown in Table 5.

TABLE 1 Composition (pbw) E1 E2 E3 E4 E5 E6 E7 E8 E9 E10 E11 E12 PolymerA 80 40 40 Polymer B 80 Polymer C 80 Polymer D 80 40 Polymer E 80Polymer F 80 Polymer G 80 40 Polymer H 80 Polymer I 80 Polymer J 80Polymer K Polymer L Polymer M Polymer N PAG 1 2 2 2 1 2 2 1 PAG 2 2 1 2PAG 3 2 1 2 PAG 4 1 1 PAG 5 2 1 2 2 2 PAG 6 2 0.5 1 1 PAG 7 2 0.5 PAG 81 0.25 2 PAG 9 0.5 Crosslinker A Dissolution inhibitor A Basic 0.1250.125 0.125 0.06 0.125 0.125 0.1 0.125 compound A Basic 0.125 0.125 0.060.025 0.125 0.125 compound B Organic acid 1 1 1 1 1 1 0.25 1 1 1 1derivative A Organic acid 0.5 0.25 derivative B Surfactant A 0.25 0.250.25 0.25 0.25 0.25 0.25 0.25 Surfactant B 0.25 0.25 0.25 0.25 UVabsorber A Solvent A 280 280 388 280 388 280 280 280 280 388 280 280Solvent B 105 105 105 105 105 105 105 105 105

TABLE 2 Composition (pbw) E13 E14 E15 E16 E17 E18 E19 E20 E21 E22 E23E24 Polymer A 40 50 50 50 Polymer B Polymer C Polymer D 20 20 10 40 4050 Polymer E Polymer F Polymer G 10 10 40 20 Polymer H 40 Polymer I 4010 10 40 10 Polymer J 40 Polymer K 80 40 Polymer L 40 Polymer M 80Polymer N 80 PAG 1 2 1 1 2 2 PAG 2 1 1 2 PAG 3 2 1 2 2 2 4 PAG 4 1 1 1 1PAG 5 1 1 1 2 2 2 1 PAG 6 1 1 1 0.5 1 PAG 7 1 0.25 0.5 PAG 8 0.5 PAG 90.5 Crosslinker A 10 Dissolution 2 2 inhibitor A Basic 0.125 0.075 0.1250.125 0.125 compound A Basic 0.125 0.125 0.05 0.125 0.125 0.125 0.1250.125 compound B Organic acid 1 1 0.5 derivative A Organic acid 1 1 0.51 0.5 1 0.5 1 derivative B Surfactant A 0.25 0.125 0.25 0.25 0.25 0.250.125 Surfactant B 0.25 0.25 0.125 0.25 0.125 0.25 0.25 UV absorber A0.25 Solvent A 280 388 388 388 280 280 388 388 280 280 388 388 Solvent B105 105 105 105 105

TABLE 3 Composition (pbw) CE1 CE2 CE3 Polymer A 80 Polymer D 80 PolymerH 80 PAG 4 1 PAG 8 2 2 PAG 9 1 2 Organic acid derivative A Organic acidderivative B 1 Basic compound A 0.125 0.125 Basic compound B 0.125Surfactant A 0.25 0.25 Surfactant B 0.25 Solvent A 388 388 388

TABLE 4 24 hr PED dimensional Sensitivity Resolution stability (mJ/cm²)(μm) Profile (nm) E1 26 0.21 rectangular −10 E2 29 0.20 rectangular −12E3 24 0.19 rectangular −9 E4 23 0.20 rectangular −10 E5 24 0.19rectangular −9 E6 23 0.19 rectangular −9 E7 25 0.20 rectangular −10 E826 0.20 rectangular 10 E9 27 0.20 rectangular 10 E10 28 0.20 rectangular10 E11 28 0.20 rectangular −9 E12 27 0.20 rectangular −9 E13 26 0.19rectangular 5 E14 26 0.20 rectangular −10 E15 28 0.20 rectangular −5 E1627 0.20 rectangular −5 E17 28 0.20 rectangular −8 E18 26 0.19rectangular 5 E19 27 0.20 rectangular 5 E20 28 0.19 rectangular 5 E21 280.21 rectangular 10 E22 26 0.20 rectangular 8 E23 27 0.20 rectangular 8E24 24 0.25 rectangular −5 (negative) CE1 35 0.22 forward tapered −30CE2 34 0.23 rounded head −30 CE3 34 0.23 forward tapered 30

TABLE 5 100 day Debris after Debris storage development afterDissolution Application stability (patterning) peeling E1 good good goodgood good E2 good good good good good E3 good good good good good E4good good good good good E5 good good good good good E6 good good goodgood good E7 good good good good good E8 good good good good good E9good good good good good E10 good good good good good E11 good good goodgood good E12 good good good good good E13 good good good good good E14good good good good good E15 good good good good good E16 good good goodgood good E17 good good good good good E18 good good good good good E19good good good good good E20 good good good good good E21 good good goodgood good E22 good good good good good E23 good good good good good E24good good good good good CE1 good good <30 days poor poor (sensitivitychanged) CE2 good good <30 days good unac- (sensitivity ceptablechanged) CE3 unacceptable good good poor poor

There have been described specific onium salts having a benzenesulfonateanion containing a sulfonate ester group. Chemical amplification typeresist compositions comprising the onium salts as the photoacidgenerator have many advantages including improved resolution, improvedfocus latitude, minimized line width variation or shape degradation evenon long-term PED, minimized defect left after coating, development andpeeling, and improved pattern profile after development. Because of highresolution, the compositions are suited for microfabrication, especiallyby deep UV lithography.

Japanese Patent Application Nos. 11-230122 and 11-230126 areincorporated herein by reference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

What is claimed is:
 1. An onium salt of formula (1):

wherein R¹ is an unsubstituted, straight, branched or cyclic alkyl groupof 1 to 10 carbon atoms, the group

an unsubstituted aryl group of 6 to 14 carbon atoms, 4-methylphenyl,4-ethylphenyl, 4-methoxyphenyl, 4-tert-butylphenyl, 2,4-dimethylphenyl,2,4,6-trimethylphenyl, or 2,4,6-triisopropylphenyl, R² which may be thesame or different is hydrogen or a an oxo- or hydroxy-substituted orunsubstituted, straight, branched or cyclic alkyl group of 1 to 6 carbonatoms, p is an integer of 1 to 5, q is an integer of 0 to 4, p+q=5, R³which may be the same or different is a substituted or unsubstituted,straight, branched or cyclic alkyl group of 1 to 10 carbon atoms orsubstituted or unsubstituted aryl group of 6 to 14 carbon atoms, M is asulfur or iodine atom, and “a” is equal to 3 when M is sulfur and equalto 2 when M is iodine.
 2. The onium salt of claim 1 of formula (1a):

wherein R¹, R², p, q and R³ are as defined above.
 3. The onium salt ofclaim 2 of formula (1a′):

wherein R¹, R², p and q are as defined above, G is an acid labile grouphaving an oxygen atom attached thereto or R²O— or (R²)₂N—, g is aninteger of 0 to 4, h is an integer of 1 to 5, g+h=5, e is an integer of1 to 3, f is an integer of 0 to 2, and e+f=3.
 4. The onium salt of claim3 wherein the acid labile group is selected from the group consisting ofgroups of the following general formulae (4) to (7), non-cyclic tertiaryalkyl groups of 4 to 20 carbon atoms, preferably 4 to 15 carbon atoms,trialkylsilyl groups whose alkyl groups each have 1 to 6 carbon atoms,oxoalkyl groups of 4 to 20 carbon atoms, and aryl-substituted alkylgroups of 7 to 20 carbon atoms,

wherein R¹⁰ and R¹¹ are independently hydrogen or straight, branched orcyclic alkyl groups of 1 to 18 carbon atoms, R¹² is a monovalenthydrocarbon group of 1 to 18 carbon atoms which may have a hetero atom,or R¹⁰ and R¹¹, R¹⁰ and R¹², or R¹¹ and R¹², taken together, may form aring, with the proviso that each of R¹⁰, R¹¹ and R¹² is a straight orbranched alkylene group of 1 to 18 carbon atoms when they form a ring,R¹³ is a tertiary alkyl group of 4 to 20 carbon atoms, a trialkylsilylgroup whose alkyl groups each have 1 to 6 carbon atoms, an oxoalkylgroup of 4 to 20 carbon atoms or a group of formula (4), and letter z isan integer of 0 to 6, R¹⁴ is a straight, branched or cyclic alkyl groupof 1 to 8 carbon atoms or substituted or unsubstituted aryl group of 6to 20 carbon atoms, h′ is equal to 0 or 1, i is equal to 0, 1, 2 or 3,satisfying 2h′+i=2 or 3, R¹⁵ is a straight, branched or cyclic alkylgroup of 1 to 8 carbon atoms or substituted or unsubstituted aryl groupof 6 to 20 carbon atoms, R¹⁶ to R²⁵ are independently hydrogen ormonovalent hydrocarbon groups of 1 to 15 carbon atoms which may containa hetero atom, or R¹⁶ to R²⁵, taken together, may form a ring, with theproviso that they are divalent hydrocarbon groups of 1 to 15 carbonatoms which may contain a hetero atom when they form a ring, or two ofR¹⁶ to R²⁵ which are attached to adjacent carbon atoms may directly bondtogether to form a double bond.
 5. The onium salt of claim 1 of thefollowing general formula (1b):

wherein R¹, R², p and q are as defined above.
 6. A photoacid generatorcontaining an onium salt of formula (1) of claim 1 for a chemicalamplification type resist composition.
 7. A photoacid generatorcontaining an onium salt of formula (1a) of claim 2 for a chemicalamplification type resist composition.
 8. A photoacid generatorcontaining an onium salt of formula (1a′) of claim 3 for a chemicalamplification type resist composition.
 9. A photoacid generatorcontaining an onium salt of formula (1b) of claim 5 for a chemicalamplification type resist composition.
 10. The onium salt according toclaim 1, wherein R¹ is methyl, ethyl, n-propyl, sec-propyl, n-butyl,sec-butyl, iso-butyl, tert-butyl, n-pentyl, sec-pentyl, cyclopentyl,n-hexyl, cyclohexyl,

phenyl, 4-methylphenyl, 4-ethylphenyl, 4-methoxyphenyl,4-tert-butylphenyl, 2,4-dimethylphenyl, 2,4,6-trimethylphenyl,2,4,6-triisopropylphenyl, 1-naphthyl or 2-naphthyl.
 11. The onium saltaccording to claim 1, wherein R¹ is phenyl, 4-methylphenyl or10-camphor.
 12. The onium salt according to claim 1, wherein methyl,ethyl, n-propyl, sec-propyl, n-butyl, sec-butyl, iso-butyl, tert-butyl,n-pentyl, sec-pentyl, cyclopentyl, n-hexyl, cyclohexyl, 2-oxopropyl,2-oxocyclopentyl, 2-oxocyclohexyl, 2-hydroxycyclopentyl or2-hydroxycyclohexyl.
 13. The onium salt according to claim 1, wherein R³is an oxo- or hydroxy-substituted or unsubstituted, straight, branchedor cyclic alkyl group of 1 to 10 carbon atoms, or an alkyl-, alkoxy-,amino- or alkylamino-substituted or unsubstituted aryl group of 6 to 14carbon atoms.
 14. The onium salt according to claim 1, wherein R³ ismethyl, ethyl, n-propyl, sec-propyl, n-butyl, sec-butyl, iso-butyl,tert-butyl, n-pentyl, sec-pentyl, cyclopentyl, n-hexyl, cyclohexyl,2-oxopropyl, 2-oxocyclopentyl, 2-oxocyclohexyl, 2-hydroxycyclopentyl,2-hydroxycyclohexyl, phenyl, 4-methylphenyl, 4-ethylphenyl,4-methoxyphenyl, 4-tert-butylphenyl, 4-tert-butoxyphenyl,4-cyclohexylphenyl, 4-cyclohexyloxyphenyl, 2,4-dimethylphenyl,2,4,6-trimethylphenyl, 2,4,6-triisopropylphenyl,3,4-bis(tert-butyoxy)phenyl, 2,4,6-triisopropylphenyl,3,4-bis(tert-butoxy)phenyl, 4-dimethylaminophenyl, 1-naphthyl or2-naphthyl.
 15. The onium salt according to claim 1, containing asulfonyloxybenzenesulfonate anion which is4-(4′-methylphenylsulfonyloxy)benzenesulfonate,4-(4′-methoxyphenylsulfonyloxy)benzenesulfonate,4-phenylsulfonyloxybenzene-sulfonate, 4-(2′, 4′,6′-trimethylphenylsulfonyloxy)benzenesulfonate,4-(2′-naphthylsulfonyloxy)benzenesulfonate,4-(10′-camphorsulfonyloxy)benzenesulfonate,4-methanesulfonyloxybenzene-sulfonate,4-(n-butanesulfonyloxy)benzenesulfonate,2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate, or2,5-bis(4′-methylphenylsulfonyloxy)benzenesulfonate.
 16. The onium saltaccording to claim 1, containing an iodonium cation which isdiphenylliodonium, bis(4-tert-butylphenyl)iodonium,4-methoxyphenylliodonium, 4-ethoxyphenylphenyl-iodonium, or4-tert-butoxyphenylphenyliodonium.
 17. The onium salt according to claim1, containing a sulfonium cation which is triphenylsulfonium,4-hydroxphenyldiphenyl-sulfonium, (4-tert-butylphenyl)diphenylsulfonium,bis(4-tert-butylphenyl)phenylsulfonium,tris(4-tert-butylphenyl)sulfonium, 4-methylphenyldiphenylsulfonium,bis(4-methylphenyl)phenylsulfonium, tris(4-methylphenyl)sulfonium,(4-tert-butoxyphenyl)diphenylsulfonium,bis(4-tert-butoxyphenyl)phenylsulfonium,tris(4-tert-butoxyphenyl)sulfonium,(3-tert-butoxyphenyl)diphenylsulfonium,bis(3-tert-butoxy-phenyl)sulfonium,diphenyl(4-thiophenoxyphenyl)sulfonium,tris(4-tert-butoxycabonylmethyloxyphenyl)sulfonium,(4-tert-butoxyphenyl)bis(4-dimethylaminophenyl)sulfonium,tris(4-methoxyphenyl)sulfonium, tris(4-ethoxyphenyl)sulfonium,tris(4-dimethylaminophenyl)sulfonium, 2-naphthyldiphenylsulfonium,dimethyl-2-naphthylsulfonium, 4-hydroxyphenyldimethylsulfonium,4-methoxyphenyldimethylsulfonium, dimethylphenylsulfonium,diphenylmethylsulfonium, trimethylsulfonium,2-oxocyclohexylcyclohexylmethylsulfonium,2-oxocyclohexyl-methyl-phenylsulfonium,2-oxocyclopenthyl-methyl-phenylsulfonium,2-oxopropyl-methyl-phenylsulfonium or tribenzylsulfonium.
 18. A resistcomposition as a photoacid generator at least one onium salt of formula(1) of claim 1:

wherein R¹ is an unsubstituted, straight, branched or cyclic alkyl groupof 1 to 10 carbon atoms or unsubstituted aryl group of 6 to 14 carbonatoms, R² which may be the same or different is a substituted orunsubstituted, straight, branched or cyclic alkyl group of 1 to 6 carbonatoms, p is an integer of 1 to 5, q is an integer of 0 to 4, p+q=5, R³which may be the same or different is a substituted or unsubstituted,straight, branched or cyclic alkyl group of 1 to 10 carbon atoms orsubstituted or unsubstituted aryl group of 6 to 14 carbon atoms, M is asulfur or iodine atom, and “a” is equal to 3 when M is sulfur and equalto 2 when M is iodine.
 19. The resist composition of claim 18 furthercomprising (G) a basic compound.
 20. The resist composition of claim 18further comprising (E) an organic acid derivative.
 21. The resistcomposition of claim 18 further comprising a propylene glycol alkylether acetate, an alkyl lactate or a mixture thereof as a solvent.
 22. Aresist composition comprising as a photoacid generator at least oneonium salt of formula (1a) of claim 2:

wherein R¹, R², p, q and R³ are as defined above.
 23. A resistcomposition comprising as a photoacid generator at least one onium saltof formula (1a′) of claim 3:

wherein R¹, R², p and q are as defined above, G is an acid labile grouphaving an oxygen atom attached thereto or R²O— or (R²)₂N—, g is aninteger of 0 to 4, h is an integer of 1 to 5, g+h=5, e is an integer of1 to 3, f is an integer of 0 to 2, and e+f=3.
 24. A resist compositioncomprising as a photoacid generator at least one onium salt of formula(1b) of claim 5:

wherein R¹, R², p and q are as defined above.
 25. A chemicalamplification resist composition comprising (A) a resin which changesits solubility in an alkaline developer under the action of an acid, and(B) at least one compound capable of generating an acid upon exposure toradiation, which is an onium salt according to claim
 1. 26. The resistcomposition of claim 25 wherein the resin (A) has substituent groupshaving C—O—C linkages whereby its solubility in an alkaline developerchanges as a result of cleavage of the C—O—C linkages under the actionof an acid.
 27. The resist composition of claim 26 wherein the resin (A)is a polymer comprising recurring units represented by the followinggeneral formula (2a′):

wherein R⁴ is hydrogen or methyl, R⁵ is a straight, branched or cyclicalkyl group of 1 to 8 carbon atoms, R⁶ is an acid labile group, R^(6a)is hydrogen or an acid labile group, R^(6a) being at least partially anacid labile group, x is 0 or a positive integer, y is a positiveinteger, satisfying x+y≦5, M and N are positive integers, L is 0 or apositive integer, satisfying 0<N/(M+N)≦0.5 and 0<(N+L)/(M+N+L)≦0.8,wherein the units of acrylate and methacrylate are contained in thepolymer in a proportion of more than 0 mol % to 50 mol % on the average,the acid labile groups are present substituted in a proportion of morethan 0 mol % to 80 mol %, on the average, based on the entire polymer,and the polymer has a weight average molecular weight of 3,000 to100,000.
 28. The resist composition of claim 25 wherein the resin (A) isa polymer containing phenolic hydroxyl groups in which hydrogen atoms ofthe phenolic hydroxyl groups are substituted by acid labile groups of atleast one type in a proportion of more than 0 mol % to 80 mol %, on theaverage, of the entire hydrogen atoms of the phenolic hydroxyl groups,said polymer having a weight average molecular weight of 3,000 to100,000.
 29. The resist composition of claim 28 wherein said acid labilegroups are groups of the following general formulae (4) to (7),non-cyclic tertiary alkyl groups of 4 to 20 carbon atoms, trialkylsilylgroups whose alkyl groups each have 1 to 6 carbon atoms, oxoalkyl groupsof 4 to 20 carbon atoms, or aryl-substituted alkyl groups of 7 to 20carbon atoms,

wherein R¹⁰ and R¹¹ are independently hydrogen or straight, branched orcyclic alkyl groups of 1 to 18 carbon atoms, R¹² is a monovalenthydrocarbon group of 1 to 18 carbon atoms which may have a hetero atom,or R¹⁰ and R¹¹, R¹⁰ and R¹², or R¹¹ and R¹², taken together, may form aring, with the proviso that each of R¹⁰, R¹¹ and R¹² is a straight orbranched alkylene group of 1 to 18 carbon atoms when they form a ring,R¹³ is a tertiary alkyl group of 4 to 20 carbon atoms, a trialkylsilylgroup whose alkyl groups each have 1 to 6 carbon atoms, an oxoalkylgroup of 4 to 20 carbon atoms or a group of formula (4), and letter z isan integer of 0 to 6, R¹⁴ is a straight, branched or cyclic alkyl groupof 1 to 8 carbon atoms or substituted or unsubstituted aryl group of 6to 20 carbon atoms, h′ is equal to 0 or 1, i is equal to 0, 1, 2 or 3,satisfying 2h′+i=2 or 3, R¹⁵ is a straight, branched or cyclic alkylgroup of 1 to 8 carbon atoms or substituted or unsubstituted aryl groupof 6 to 20 carbon atoms, R¹⁶ to R²⁵ are independently hydrogen ormonovalent hydrocarbon groups of 1 to 15 carbon atoms which may containa hetero atom, or R¹⁶ to R²⁵, taken together, may form a ring, with theproviso that they are divalent hydrocarbon groups of 1 to 15 carbonatoms which may contain a hetero atom when they form a ring, or two ofR¹⁶ to R²⁵ which are attached to adjacent carbon atoms may directly bondtogether to form a double bond.
 30. The resist composition of claim 25wherein the resin (A) is a polymer comprising recurring unitsrepresented by the following general formula (2):

wherein R⁴ is hydrogen or methyl, R⁵ is a straight, branched or cyclicalkyl group of 1 to 8 carbon atoms, x is 0 or a positive integer, y is apositive integer, and x+y is up to 5, in which hydrogen atoms of thephenolic hydroxyl groups are substituted by acid labile groups of atleast one type in a proportion of more than 0 mol % to 80 mol %, on theaverage, of the entire hydrogen atoms of the phenolic hydroxyl groups,said polymer having a weight average molecular weight of 3,000 to100,000.
 31. The resist composition of claim 30 wherein the resin (A) isthe polymer of formula (2) in which some of the hydrogen atoms of thephenolic hydroxyl groups are substituted by acid labile groups of atleast one type, and the hydrogen atoms of the remaining phenolichydroxyl groups are crosslinked within a molecule and/or betweenmolecules, in a proportion of more than 0 mol % to 50 mol %, on theaverage, of the entire phenolic hydroxyl groups on the polymer, withcrosslinking groups having C—O—C linkages represented by the followinggeneral formula (3a) or (3b):

wherein each of R⁷ and R⁸ is hydrogen or a straight, branched or cyclicalkyl group of 1 to 8 carbon atoms, or R⁷ and R⁸, taken together, mayform a ring, and each of R⁷ and R⁸ is a straight or branched alkylenegroup of 1 to 8 carbon atoms when they form a ring, R⁹ is a straight,branched or cyclic alkylene group of 1 to 10 carbon atoms, letter a′ isan integer of 1 to 7, letter b is 0 or an integer of 1 to 10, A is an(a′+1)-valent aliphatic or alicyclic saturated hydrocarbon group,aromatic hydrocarbon group or heterocyclic group of 1 to 50 carbonatoms, which may be separated by a hetero atom and in which some of thehydrogen atoms attached to carbon atoms may be replaced by hydroxyl,carboxyl, carbonyl or halogen, B is —CO—O—, —NHCO—O— or —NHCONH—.
 32. Achemical amplification resist composition comprising (A) a resin whichchanges its solubility in an alkaline developer under the action of anacid, (B) at least one compound capable of generating an acid uponexposure to radiation, which is an onium salt according to claim 1, and(C) at least one compound capable of generating an acid upon exposure toradiation, other than an onium salt according to claim
 1. 33. A processfor forming a pattern, comprising the steps of: applying the resistcomposition of claim 18 onto a substrate to form a coating, heattreating the coating and exposing the coating to high energy radiationwith a wavelength of up to 300 nm or electron beam through a photo-mask,optionally heat treating the exposed coating, and developing the coatingwith a developer.